He wrote this letter for al-Hasan ibn `Ali 1 (his son - peace be upon them), when Amir al-mu'minin encamped at al-Hadirin on his way back from Siffin.
From the father who is (shortly) to die, who acknowledges the hardships of the times, who has turned away from life, who has submitted himself to the (calamities of) time, who realizes the evils of the world, who is living in the abodes of the dead and is due to depart from them any day; to the son who yearns for what is not to be achieved, who is treading the path of those who have died, who is the victim of ailments, who is entangled in the (worries of the) days, who is a target of hardships, a slave of the world, a trader of its deception, a debtor of wishes, a prisoner of mortality, an ally of worries, a neighbour of grief, a victim of distresses, who has been overpowered by desires, and who is a successor of the dead.
Now (you should know that) what I have learnt from the turning away of this world from me, the onslaught of time over me and the advancing of the next world towards me is enough to prevent me from remembering anyone except myself and from thinking beyond myself. But when I confined myself to my own worries leaving the worries of others, my intelligence saved me and protected me from my desires. It clarified to me my affairs and led me to seriousness wherein there was no trickery and truth which was not tarnished by falsehood. Here, I found you a part of myself, rather I found you my whole, so much so that if anything befell you, it was as though it befell me and if death came to you it was as though it came to me. Consequently, your affairs meant to me what my own matters meant to me. So, I have written this piece of advice (to you) as an instrument of seeking help through it, whether I remain alive for you or cease to exist.
I advise you to fear Allah, O my child, abide by His commands, fill your heart with remembrance of Him and cling to hope from Him. No connection is more reliable than the connection between you and Allah provided you take hold of it. Enliven your heart with preaching, kill it by denial, energise it with firm belief, enlighten it with wisdom, humiliate it by recalling death, make it believe in mortality, make it see the misfortunate of this world, make it fear the authority of the time and the severity of some changes during the nights and the days, place before it the events of past people, recall to it what befell those who were before you and walk among their cities and ruins, then see what they did and from what they have gone away and where they have gone and stayed. You will find that they departed from (their) friends and remain in loneliness. Shortly, you too will be like one of them. Therefore, plan for your place of stay and do not sell your next life with this world.
Give up discussing what you do not know and speaking about what does not concern you. Keep off track from which you fear to go astray because refraining (from moving) when fear of straying is better than embarking on dangers. Ask others to do good; you will thus be among good doers. Desist others from evil with your action as well as speech and keep off, to the best of your ability, from he who commits it. Struggle for Allah as is His due; and the insults of a reviler should not stop you in matters of Allah. 
Leap into dangers for the sake of right wherever it be. Acquire insight into religious law. Accustom yourself to endure hardships since the best trait of character is endurance in matters of right. In all affairs resign yourself to Allah, because you will thus be resigning yourself to a secure shelter and a strong protector. You should ask only from your Lord because in His hand is all the giving and depriving. Seek good (from Allah) as much as you can. Understand my advice an do not turn away from it, because the best saying is that which benefits. Know that there is no good in that knowledge which does not benefit, and if knowledge is not made use of then its acquisition is not justified.
O my child, when I noticed I was of goodly age and noticed I was increasing in weakness I hastened with my will for you and wrote down prominent points of it in case death overtook before I divulged to you what I have in my heart, or in case my wit be affected as my body has been affected, or forces of passions or mischief of the world overtake you making you like a stubborn camel. Certainly, the heart of a young man is like uncultivated land. It accepts whatever is strewn on it. So, I hastened to mould you properly before your heart hardened up and your mind became occupied, so you might be ready to accept through your intelligence the results of the experience of others and be saved from going through these experiences yourself. In this way, you would avoid the hardship of seeking them and the difficulties of experimenting. Thus, you are getting to know what we had experienced and even those things are becoming clear to you which we might have missed.
O my child, even though I have not reached the age which those before me have, yet I looked into their behaviour and thought over events of their lives. I walked among their ruins till I was as one of them. In fact, by virtue of those of their affairs that have become known to me it is as though I have lived with them from the first to the last. I have therefore been able to discern the impure from the clean and the benefit from the harm.
I have selected for you the choicest of those matters and collected for you their good points and have kept away from you their useless points. Since I feel for your affairs as a living father should feel and I aim at giving you training, I thought it should be at a time when you are advancing in age and new on the stage of the world, possessing upright intention and clean heart and that I should begin with the teaching of the Book of Allah, and its interpretation, the laws of Islam and its commands, its lawful matters and unlawful matters and that I should not go beyond these for you. Then I feared lest you should get confused as other people had been confused on account of their passions and (different) views. Therefore, in spite of my dislike for you being so warned, I thought it better for me to make this position strong rather than leave you in a position where I do not regard you safe from falling into destruction. I hoped that Allah would help you in your straightforwardness and guide you in your resoluteness. Consequently, I wrote this piece of my will for you.
Know O my child, what I love most for you to adopt from my will is to fear Allah, to confine yourself to what Allah has made obligatory on you, and to follow the actions of your forefathers and the virtuous people of your household, because they did not fall short in seeing for themselves what you will see for yourself, and they did about their affairs as you would like to think (about your affairs). Thereafter, their thinking led them to discharge the obligations they came to know of and to desist from what they were not required to do. If your heart does not accept this without acquiring knowledge as they acquired it, then your search should first be by way of understanding and learning and not by falling into doubts or getting entangled in quarrels.
And before you probe into this, you should begin by seeking your Allah's help and turning to Him for competence and keeping aloof from everything that throws you into doubt or flings you towards misguidance. When you have made sure that your heart is clean and humble and your thoughts have come together and you have only one thought which is about this matter, then you will see what I have explained to you; but if you have not been able to achieve that peace of observation and thinking which you would like to have, then know that you are only stamping the ground like a blind she-camel and falling into darkness while a seeker of religion should not grope in the dark or create confusion. It is better to avoid this.
Appreciate my advice, O my child, and know He Who is the Master of death is also the Master of life, that the Creator causes death as well; that He Who destroys is also the restorer of life and that He Who inflicts disease is also the curer. This world continues in the way Allah has made it with regard to its pleasures, trials, rewards on the Day of Judgement and all that He wishes and you do not know. If anything of this advice is not understood by you then attribute it to your ignorance of it, because when you were first born you were born ignorant. Thereafter, you acquired knowledge. There are many matters of which you are ignorant and in which your sight first wonders and your eye wanders then after this you see them. Therefore, cling to Him Who created you, fed you and put you in order. Your worship should be for Him, your eagerness should be towards Him and your fear should be of Him.
Know O my child, that no one received messages from Allah, the Glorified, as the Prophet (S) did. Therefore, regard him as your forerunner and leader towards deliverance. Certainly, I shall spare no effort in giving you advice and surely even if you try, you cannot acquire that insight for your welfare as I have for you.
Know O my child, if there had been a partner with your Lord, his messengers too should have come to you and you would have seen signs of his authority and power and have known his deeds and qualities. But He is only One God as He has described Himself. No one can dispute with Him in His authority. He is from ever and will be for ever. He is before all things without any beginning. He will remain after all things without any end. He is far too great to have His divinity proved by the encompassing heart or eye. When you have understood this then you should do what is done by him who is like you by way of his low position, his lack of authority, his increasing incapability, and his great need of his Lord for seeking His obedience,fearing His chastisement and apprehending His anger, because He does not command you save for virtue and does not refrain you save from evil.
O my child, I have informed you about the world, its condition,decay and its passing away and I have informed you of the next world and of what has been provided in it for its people. I have recounted to you parables about it so that you may draw instruction from them and act upon them. The example of those who have understood the world is like those travellers who, being disgusted with drought-stricken places set off for greenery and a fruitful place. Then they endure difficulties on the way, separation from friends, hardships of the journey and unwholesome food in order to reach their fields of plenty and place of stay. Consequently, they do not feel any pain in all this and do not regard any expenditure to be waste. 
Nothing is more lovable to them than what takes them near their goal and carries them closer to their place of stay. (Against this), the example of those who are deceived by this world is like the people who were in a green place but they became disgusted with it and went to a drought-stricken place. Therefore, for them nothing is more detestable or abominable than to leave the place where they were to go to a place which they will reach unexpectedly and for which they are heading.
O my child, make yourself the measure (for dealings) between you and others. Thus, you should desire for others what you desire for yourself and hate for others what you hate for yourself. Do not oppress as you do not like to be oppressed. Do good to others as you would like good to be done to you. Regard bad for yourself whatever you regard bad for others. Accept that (treatment) from others which you would like others to accept from you. Do not talk about what you do not know even though what you know be very little. Do not say to others what you do not like to be said to you.
Know that self-admiration is contrary to propriety (of action) and is a calamity for the mind. Therefore, increase your striving and do not become a treasurer for (wealth to be inherited by) others. When you have been guided on the right path humble yourself before Allah as much as you can.
Know in front of you lies a road of long distance and severe hardship and you cannot avoid seeking it. Take your requirements of provision keeping the burden light. Do not load your back beyond your power lest its weight become a mischief for you. Whenever you come across a needy person who can carry for you your provision to hand it back to you on the Day of Judgement when you will need it, then accept him as a good opportunity and get him to carry it. Put in that provision as much-as you are able to, for it is likely that if you may need him (afterwards), you may not get hold of him. If a person is willing to borrow from you in the days of your affluence to pay it back to you at the time of your need then make use of this opportunity.
Know that in front of you lies an impassable valley wherein the light-burdened man will be in a better condition than the heavy-burden one, and the slow- paced would be in a worse condition than the swift-paced. Your terminating point at the other end of this passage will necessarily be either Paradise or Hell. Therefore, investigate for yourself before alighting, and prepare the place before getting down, because after death there can be no preparation nor return to this world.
Know that He Who owns the treasuries of the heavens and of the earth has permitted you to pray to Him and has promised you acceptance of the prayer. He has commanded you to beg from Him in order that He may give you and to seek His mercy in order that He may have mercy on you. He has not placed any thing between you and Him that may veil Him from you. He has not required you to get a mediator for you to Him, and if you err, He has not prevented you from repentance. He does not hasten with punishment. He does not taunt you for repenting, nor does He humiliate you when humiliation is more appropriate for you. He has not been harsh in accepting repentance. He does not severely question you about your sins. He does not disappoint you of His mercy. Rather He regards abstention from sin as a virtue. He counts your one sin as one while He counts your one virtue as ten.
He has opened for you the door of repentance. Therefore, whenever you call Him He hears your call, and whenever you whisper to Him He knows the whisper. You place before Him your needs, unveil yourself before Him, complain to Him of your worries, beseech Him to remove your troubles, seek His help in your affairs and ask from the treasuries of His mercy that which no one else has power to give, namely length of life, health of body and increase in sustenance. Then He has placed the keys of His treasuries in your hands in the sense that He has shown you the way to ask Him.
Therefore, wherever you wish, open the doors of His favour with prayer, and let abundant rains of His mercy fall on you. Delay in acceptance of prayer should not disappoint you because grant of prayer is according to the measure of (your) intention. Sometimes acceptance (of prayer) is delayed with a view to its being a source of greater reward to the asker and of better gifts to the expectant. Sometimes you ask for a thing but it is not given to you, and a better thing is given to you later, or a thing is taken away from you for some greater good of yours, because sometimes you ask for a thing which contains ruin for your religion if it is given to you. Therefore, your request should be for things whose beauty should be lasting and whose burden should remain away from you. As for wealth it will not last for you nor will you live for it.
O my child, know that you have been created for the next world, not for this world, for destruction (in this world) not for lasting, and for dying not for living. You are in a place which does not belong to you, a house for making preparations and a passage towards the next world. You are being chased by death from which the runner -away cannot escape, as it would surely overtake him. So, be on guard against it lest it overtakes you at a time when you are in a sinful state and you are thinking of repenting but it creates obstruction between you and repentance. In such a case you will ruin yourself.
O my child, remember death very much and the place where you have to go suddenly and reach after death, so that when it comes you are already on your guard against it and have prepared yourself for it and it does not come to you all of a sudden and surprise you. Beware, lest you become deceived by the leanings of the people towards worldly attraction and their rushing upon it. Allah has warned you about it and the world has informed you of its mortal character and unveiled to you its evils.
Surely, those (who go) after it are like barking dogs or devouring carnivore who hate each other. The stronger among them eat away the weaker and the big among them tramples over the small. Some are like tied cattle and some like untied cattle who have lost their wits and are running in unknown directions. They are flocks of calamities wandering in rugged valleys. There is no herdsman to detain them nor any tenderer to take them to grazing. The world has put them on the track of blindness and taken away their eyes from the beacons of guidance. They have therefore perplexed in its bewilderings and sunk in its pleasures. They took it as a god so it played with them. They too played with it and forgot what is beyond it.
Darkness is disappearing gradually. Now it is as though travellers have got down and the hasteners will soon meet. Know, O my child, that everyone who is riding on the carriage of night and day is being carried by them even though he may be stationary,and he is covering the distance even though he is staying and resting.
Know with certainty you cannot achieve your desire and exceed your destined life. You are on the track of those before you. Therefore, be humble in seeking and moderate in earning because often seeking leads to deprivation. Every seeker of livelihood does not get it, nor is everyone who is moderate in seeking deprived. Keep yourself away from every low thing even though they may take you to your desired aims, because you will not get any return for your own respect which you spend. Do not be the slave of others for Allah had made you free. There is no good in good which is achieved through evil and no good in comfort that is achieved through (disgracing) hardship.
Beware lest bearers of greed should carry you and make you descend down to the springs of destruction. If you can manage that there be no wealthy person between yourself and Allah, do so, because in any case you will find what is for you and get your share. A little received directly from Allah the Glorified, is more dignified than that which is more but is received through (the obligation of) His creatures, although (really) all is from Allah.
It is easier to rectify what you miss by silence than to secure what you lose by speaking. Whatever is in a pot can be retained by closing the lid. I should prefer you to retain what is in your hands rather to seek what is in other's hands. Bitterness of disappointment is better than seeking from people. Manual labour. with chastity is better than the riches of a vicious life. A man is the best guard of his own secrets. Often a man strives for what harms him. He who speaks much speaks nonsense. Whoever ponders perceives. Associate with people of virtue; you will become one of them. Keep aloof from people of vice; you will remain safe from them. The worst food is that which is unlawful. Oppressing the weak is the worst oppression.
Where leniency is unsuitable, harshness is lenience. Often cure is illness and illness is cure. Often the ill-wisher gives correct advice while the well-wisher cheats. Do not depend upon hopes because hopes are the mainstay of fools. It is wise to preserve one's experience. Your best experience is that which teaches you a lesson. Make use of leisure before it changes into (the hour of) grief. Every seeker does not achieve (what he seeks); and every departed does not return. To lose provision and to earn evil for the Day of Judgement means ruin. 
Every matter has a consequence. What is destined for you will shortly come to you. A trader undertakes a risk. Often a small quantity is more beneficial than a large quantity. There is no good in an ignoble helper, nor in a suspicious friend. Be compliant with the world as long as it is in your grip. Do not put yourself to risk as regards anything in expectation for more than that. Beware lest the feeling of enmity should overpower you.
Bear yourself towards your brother in such a way that if he disregards kinship you keep to it; when he turns away be kind to him and draw near to him; when he withholds spend for him; when he goes away approach him; when he is harsh be lenient; when he commits wrong think of (his) excuse for it, so much so as though you are a slave of him and he is the benevolent master over you. But take care that this should not be done inappropriately, and that you should not behave so with an undeserving person. Do not take the enemy of your friend as a friend because you will thus antagonize your friend. Give true advice to your brother, be it good or bitter. Swallow your anger because I did not find a sweeter thing than it in the end, and nothing more pleasant in consequence. Be lenient to him who is harsh to you for it is likely that he will shortly become lenient to you. Treat your enemy with favours, because this is sweeter of the two successes (the success of revenge and the success of doing favour).
If you intend to cut yourself off from a friend leave some scope for him from your side by which he may resume friendship if it occurs to him some day. If anyone has a good idea about you prove it to be true. Do not disregard interests of your brother depending upon your terms with him, for he is not your brother if you disregard his interests. Your household should not become the most miserable people through you. Do not lean towards him who turns away from you. Your brother should not be more firm in his disregard of kinship than you in paying regard to it, and you should exceed in doing good to him than is evil to you. Do not feel too much the oppression of a person who oppresses you, because he is only busy in harming himself and benefiting you. The reward of him who pleases you is not that you displease him.
Know O my child, that livelihood is of two kinds - a livelihood that you seek and a livelihood that seeks you, which is such that if you do not reach it, it will come to you. How bad it is to bend down at the time of need and to be harsh in riches. You should have from this world only that with which you can adorn your permanent abode. If you cry over what has gone out of your hands then also cry for what has not at all come to you. Infer about what has not yet happened from what has already happened, because occurrences are ever similar. Do not be like those whom preaching does not benefit unless you inflict pain on them, because the wise take instruction from teaching while beasts learn only from beating.
Ward off from yourself the onslaught of worries by firmness of endurance and purity of belief. He who gives up moderation commits excess. A companion is like a relation. A friend is he whose absence also proves the friendship. Passion is a partner of distress. Often the near ones are remoter than the distant ones, and often the distant ones are nearer than the near ones. A stranger is he who has no friend. He who transgresses right narrows his own passage. He who stays in his position remains constant upon it. The most trustworthy intermediary is that which you adopt between yourself and Allah the Glorified. He who does not care for your interests is your enemy. When greed leads to ruin deprivation is an achievement. Not every defect can be reviewed, and not every opportunity recurs.
Often a person with eyes misses the track while a blind person finds the correct path. Delay an evil because you will be able to hasten it whenever you desire. The disregard of kinship of the ignorant is equal to the regard for kinship of the wise. Whoever takes the world to be safe, it will betray him. Whoever regards the world as great, it will humiliate him. Every one who shoots does not hit. When authority changes, the time changes too. Consult the friend before adopting a course and the neighbour before taking a house. Beware, lest you mention in your speech what may rouse laughter even though you may be relating it from others.
Do not consult women because their view is weak and their determination unstable. Cover their eyes by keeping them under the veil because strictness of veiling keeps them for long. Their coming out is not worse than your allowing an unreliable man to visit them. If you can manage that they should not know anyone other than you, do so. Do not allow a woman matters other than those about hereself, because a woman is a flower not an administrator. Do not pay her regard beyond herself. Do not encourage her to intercede for others. Do not show suspicion out of place, because this leads a correct woman to evil and a chaste woman to deflection. For everyone among your servants fix a work for which you may hold him responsible. In this way, they will not fling the work one over the other. Respect your kinsmen because they are your wings with which you fly, the origin towards which you return and your hands with which you attack. Place your religion and your world at Allah's disposal and beg Him to ordain the best for you in respect of the near and the far, this world and the next; and that is an end to the matter.