The Prophet (S) is the trustee of Allah's revelation, the Last of His Prophets. the giver of tidings of His mercy and the warner for His chastisement.
O people! The most rightful of all persons for this matter (namely the caliphate) is he who is most competent among them to maintain it, and he who knows best Allah's commands about it. If any mischief is created by a mischief-monger, he will be called upon to repent. If he refuses, he will be fought. 
By my life, 1 if the question of Imamah was not to be decided unless all the people were present, then there would be no such case. But those who agreed about it imposed the decision on those who were absent, so much so that he who was present could not dissent and the one who was absent could not choose (any one else). Know that I shall fight two persons - one who claims what is not his and the other who ignores what is obligatory upon him.
O creatures of Allah! I advise you to have fear of Allah because it is the best advice to be mutually given by persons, and the best of all things before Allah. The door of war has been opened between you and the other Muslims. And this banner will be borne only by him who is a man of sight, of endurance and of knowledge of the position of rightfulness. Therefore, you should go ahead with what you are ordered and desist from what you are refrained. Do not make haste in any matter till you have clarified it. For in the case of every matter which you dislike we have a right to change it.
Know that this world which you have started to covet and in which you are interested, and which sometimes enrages you and sometimes pleases you is not your (permanent) abode, nor the place of your stay for which you might have been created, nor one to which you have been invited. Know that it will not last for you nor will you live along with it. If anything out of this world deceives you (into attraction), its evils warn you too. 
You should give up (the objects of) its deceits in favour of (the objects of) its warning and (the objects of) its attractions in favour of (the objects of) its terrors. And while here in it, advance towards that house to which you have been called, and turn away your hearts from the world. None of you should cry like a maid slave over anything which she has been deprived of. Seek the perfection of Allah's bounty over you by endurance in obedience to Allah and in guarding what He has asked you to guard, namely His Book.
Know that the loss of anything of this world will not harm you, if you have guarded the principles of your religion. Know also that after the loss of your religion nothing of this world for which you have cared will benefit you. May Allah carry our hearts and your hearts towards the right and may He grant us and you endurance.
(1) Al-Harrani, Tuhaf, 130;