Jami at-Tirmidhi 27543
In-book no 1763حَدَّثَنَا ابْنُ أَبِي عُمَرَ، حَدَّثَنَا سُفْيَانُ بْنُ عُيَيْنَةَ، عَنْ عُبَيْدِ اللَّهِ، نَحْوَهُ بِمَعْنَاهُ إِلاَّ أَنَّهُ قَالَ قَالَ عُمَرُ بْنُ عَبْدِ الْعَزِيزِ هَذَا حَدُّ مَا بَيْنَ الذُّرِّيَّةِ وَالْمُقَاتِلَةِ . وَلَمْ يَذْكُرْ أَنَّهُ كَتَبَ أَنْ يُفْرَضَ . قَالَ أَبُو عِيسَى حَدِيثُ إِسْحَاقَ بْنِ يُوسُفَ حَدِيثٌ حَسَنٌ صَحِيحٌ غَرِيبٌ مِنْ حَدِيثِ سُفْيَانَ الثَّوْرِيِّ .
Another chain with similar, but he (Nafi') said: "Umar said: 'This is the limit that distinguished between children and soldiers.'" And he did not mention him writing about the salary The Hadith of Ishaq bin Yusuf is a Hasan Sahih Gharib Hadith as narration of Sufyan Ath-Thawri