Tirmidhi Book 23, Hadith 1711

حَدَّثَنَا مُحَمَّدُ بْنُ الْوَزِيرِ الْوَاسِطِيُّ، حَدَّثَنَا إِسْحَاق بْنُ يُوسُفَ الْأَزْرَقُ، عَنْ سُفْيَانَ، عَنْ عُبَيْدِ اللَّهِ بْنِ عُمَرَ، عَنْ نَافِعٍ، عَنْ ابْنِ عُمَرَ، قَالَ:‏‏‏‏ عُرِضْتُ عَلَى رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فِي جَيْشٍ وَأَنَا ابْنُ أَرْبَعَ عَشْرَةَ فَلَمْ يَقْبَلْنِي، ‏‏‏‏‏‏ثُمَّ عُرِضْتُ عَلَيْهِ مِنْ قَابِلٍ فِي جَيْشٍ وَأَنَا ابْنُ خَمْسَ عَشْرَةَ فَقَبِلَنِي ، ‏‏‏‏‏‏قَالَ نَافِعٌ:‏‏‏‏ فَحَدَّثْتُ بِهَذَا الْحَدِيثِ عُمَرَ بْنَ عَبْدِ الْعَزِيزِ، ‏‏‏‏‏‏فَقَالَ:‏‏‏‏ هَذَا حَدُّ مَا بَيْنَ الصَّغِيرِ وَالْكَبِيرِ، ‏‏‏‏‏‏ثُمَّ كَتَبَ أَنْ يُفْرَضَ لِمَنْ بَلَغَ الْخَمْسَ عَشْرَةَ .

Narrated Nafi: That Ibn 'Umar said: I was reviewed before army, and I was fourteen years old, but he did not accept me. Then I was reviewed before him later in army while I was fifteen years old, and he accepted me. Nafi said: I narrated this Hadith to 'Umar bin 'Abdul-'Aziz and he said: 'This is the limit that distinguishes between youth and manhood.' The he wrote to give salaries to whoever reached fifteen years of age.