The Messenger of Allah ﷺ inspected me on the battlefield on the Day of Uhud, and I was fourteen years old. He did not allow me (to take part in the fight). He inspected me on the Day of Khandaq-and I was fifteen yearsold, and he permitted me (to fight), Nafi' said: I came to 'Umar b. 'Abd al-'Aziz who was then Caliph, and narrated this tradition to him. He said: Surely, this is the demarcation between a minor and a major. So he wrote to his governors that they should pay subsistence allowance to one who was fifteen years old, but should treat those of lesser age among children. (Using translation from Muslim 1868a)
أَنَّ رَسُولَ اللهِ ﷺ عَرَضَهُ يَوْمَ أُحُدٍ لِلْقِتَالِ قَالَ وَأَنَا ابْنُ أَرْبَعَ عَشْرَةَ سَنَةً فَلَمْ يُجِزْنِي قَالَ ثُمَّ عَرَضَنِي يَوْمَ الْخَنْدَقِ وَأَنَا ابْنُ خَمْسَ عَشْرَةَ سَنَةً فَأَجَازَنِي قَالَ نَافِعٌ فَقَدِمْتُ عَلَى عُمَرَ بْنِ عَبْدِ الْعَزِيزِ وَهُوَ إِذْ ذَاكَ خَلِيفَةٌ فَحَدَّثْتُ هَذَا الْحَدِيثَ فَقَالَ إِنَّ هَذَا الْحَدَّ بَيْنَ الصَّغِيرِ وَالْكَبِيرِ ثُمَّ كَتَبَ إِلَى عُمَّالِهِ بِأَنْ يَفْرِضُوا لِمَنْ بَلَغَ خَمْسَ عَشْرَةَ سَنَةً وَمَا كَانَ دُونَ ذَلِكَ أَنْ يَجْعَلُوهُ مَعَ الْعِيَالِ