The Book of Purification
1/9. Chapter:
Mentioning The Fitrah (The Natural Inclination Of Man) - Circumcision
Sunan an-Nasai
أَخْبَرَنَا الْحَارِثُ بْنُ مِسْكِينٍ، قِرَاءَةً عَلَيْهِ وَأَنَا أَسْمَعُ، عَنِ ابْنِ وَهْبٍ، عَنْ يُونُسَ، عَنِ ابْنِ شِهَابٍ، عَنْ سَعِيدِ بْنِ الْمُسَيَّبِ، عَنْ أَبِي هُرَيْرَةَ، عَنْ رَسُولِ اللَّهِ صلى الله عليه وسلم قَالَ " الْفِطْرَةُ خَمْسٌ الاِخْتِتَانُ وَالاِسْتِحْدَادُ وَقَصُّ الشَّارِبِ وَتَقْلِيمُ الأَظْفَارِ وَنَتْفُ الإِبْطِ " .
It was narrated from Abu Hurairah that the Messenger of Allah (ﷺ) said: "The Fitrah are five: Circumcision, removing the pubes, trimming the mustache, clipping the nails, and plucking the armpit hairs."
Reference : Sunan an-Nasa'i 9In-book reference : Book 1, Hadith 9English translation : Vol. 1, Book 1, Hadith 9