The Book of Virtues
حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، حَدَّثَنَا الْمُغِيرَةُ، - يَعْنِي ابْنَ عَبْدِ الرَّحْمَنِ الْحِزَامِيَّ - عَنْ أَبِي الزِّنَادِ، عَنِ الأَعْرَجِ، عَنْ أَبِي هُرَيْرَةَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " اخْتَتَنَ إِبْرَاهِيمُ النَّبِيُّ عَلَيْهِ السَّلاَمُ وَهُوَ ابْنُ ثَمَانِينَ سَنَةً بِالْقَدُومِ " .Abu Huraira reported Allah's Messenger (ﷺ) as having said that Ibrahim (as) circumcised himself with the help of an adze when he was eighty years old
From Sahih Muslim, whose reports the scholars accept as authentic.