Sahih Muslim Book - 33, Hadith - 4837

حَدَّثَنَا مُحَمَّدُ بْنُ عَبْدِ اللَّهِ بْنِ نُمَيْرٍ حَدَّثَنَا أَبِى حَدَّثَنَا عُبَيْدُ اللَّهِ عَنْ نَافِعٍ عَنِ ابْنِ عُمَرَ قَالَ عَرَضَنِى رَسُولُ اللَّهِ -صلى الله عليه وسلم- يَوْمَ أُحُدٍ فِى الْقِتَالِ وَأَنَا ابْنُ أَرْبَعَ عَشْرَةَ سَنَةً فَلَمْ يُجِزْنِى وَعَرَضَنِى يَوْمَ الْخَنْدَقِ وَأَنَا ابْنُ خَمْسَ عَشْرَةَ سَنَةً فَأَجَازَنِى. قَالَ نَافِعٌ فَقَدِمْتُ عَلَى عُمَرَ بْنِ عَبْدِ الْعَزِيزِ وَهُوَ يَوْمَئِذٍ خَلِيفَةٌ فَحَدَّثْتُهُ هَذَا الْحَدِيثَ فَقَالَ إِنَّ هَذَا لَحَدٌّ بَيْنَ الصَّغِيرِ وَالْكَبِيرِ. فَكَتَبَ إِلَى عُمَّالِهِ أَنْ يَفْرِضُوا لِمَنْ كَانَ ابْنَ خَمْسَ عَشْرَةَ سَنَةً وَمَنْ كَانَ دُونَ ذَلِكَ فَاجْعَلُوهُ فِى الْعِيَالِ.

It was narrated that Ibn 'Umar said: "The Messenger of Allah (s.a.w) inspected me on the day of (the battle of) Uhud, when I was fourteen years old, and he did not allow me to take part in the fighting. He inspected me on the day of (the battle of) Al-Khandaq, when I was fifteen years old, and he allowed me (to take part in the fighting)." Nafi' said: "I came to 'Umar bin 'Abdul-'Aziz, who was the caliph at that time, and I narrated this Hadith to him. He said: 'This is the demarcation between a minor and an adult.' He wrote to his agents telling them to pay a stipend to all those over the age of fifteen, and to regard all those under that age as children."