Sahih Muslim 1812 a
It has been narrated on the authority of Yazid b. Hurmuz that Najda wrote to Ibn Abbas inquiring of him five things. Ibn Abbas said:
If I had not the fear of committing (sin) for concealing the knowledge I would not have written to him. Najda wrote to him saying (after praising the Almighty and invoking blessings on the Prophet): Tell me whether the Messenger of Allah (ﷺ) took women to participate with him in Jihad; (if he did), whether he allotted them a regular share from the booty; whether he killed the children of (the enemy in the war), how long an orphan would be entitled to consideration as such, and for whom the Khums (fifth part of the booty) was booty. Ibn Abbas wrote to him: You have written asking me whether the Messenger of Allah (ﷺ) took women with him to participate in Jihad. He did take them to the battle and sometimes he fought along with them. They would treat the wounded and were given a reward from the booty, but he did not assign any regular share for them. And the Messenger of Allah (ﷺ) did not kill the children of the enemy, so you should not kill the children. Also you have written to me asking me when the orphanhood of an orphan comes to an end. By my life, if a man has become bearded but is still incapable of getting his due from others or fulfilling his obligation towards them, (he is yet an orphan to be treated as such), but when he can look after his interests like grown-up people, he is no longer an orphan. And you have written to me inquiring about Khums as to whom it is meant for. (In this connection) we (the kinsmen of the Messenger of Allah) used to say: It is for us, but those people (i.e. Banu Umayya) have denied it to us.
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ بْنِ قَعْنَبٍ، حَدَّثَنَا سُلَيْمَانُ، - يَعْنِي ابْنَ بِلاَلٍ - عَنْ جَعْفَرِ بْنِ مُحَمَّدٍ، عَنْ أَبِيهِ، عَنْ يَزِيدَ بْنِ هُرْمُزَ، أَنَّ نَجْدَةَ، كَتَبَ إِلَى ابْنِ عَبَّاسٍ يَسْأَلُهُ عَنْ خَمْسِ، خِلاَلٍ ‏.‏ فَقَالَ ابْنُ عَبَّاسٍ لَوْلاَ أَنْ أَكْتُمَ، عِلْمًا مَا كَتَبْتُ إِلَيْهِ ‏.‏ كَتَبَ إِلَيْهِ نَجْدَةُ أَمَّا بَعْدُ فَأَخْبِرْنِي هَلْ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يَغْزُو بِالنِّسَاءِ وَهَلْ كَانَ يَضْرِبُ لَهُنَّ بِسَهْمٍ وَهَلْ كَانَ يَقْتُلُ الصِّبْيَانَ وَمَتَى يَنْقَضِي يُتْمُ الْيَتِيمِ وَعَنِ الْخُمْسِ لِمَنْ هُوَ فَكَتَبَ إِلَيْهِ ابْنُ عَبَّاسٍ كَتَبْتَ تَسْأَلُنِي هَلْ كَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يَغْزُو بِالنِّسَاءِ وَقَدْ كَانَ يَغْزُو بِهِنَّ فَيُدَاوِينَ الْجَرْحَى وَيُحْذَيْنَ مِنَ الْغَنِيمَةِ وَأَمَّا بِسَهْمٍ فَلَمْ يَضْرِبْ لَهُنَّ وَإِنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم لَمْ يَكُنْ يَقْتُلُ الصِّبْيَانَ فَلاَ تَقْتُلِ الصِّبْيَانَ وَكَتَبْتَ تَسْأَلُنِي مَتَى يَنْقَضِي يُتْمُ الْيَتِيمِ فَلَعَمْرِي إِنَّ الرَّجُلَ لَتَنْبُتُ لِحْيَتُهُ وَإِنَّهُ لَضَعِيفُ الأَخْذِ لِنَفْسِهِ ضَعِيفُ الْعَطَاءِ مِنْهَا فَإِذَا أَخَذَ لِنَفْسِهِ مِنْ صَالِحِ مَا يَأْخُذُ النَّاسُ فَقَدْ ذَهَبَ عَنْهُ الْيُتْمُ وَكَتَبْتَ تَسْأَلُنِي عَنِ الْخُمْسِ لِمَنْ هُوَ وَإِنَّا كُنَّا نَقُولُ هُوَ لَنَا ‏.‏ فَأَبَى عَلَيْنَا قَوْمُنَا ذَاكَ ‏.‏