Abu Hurayrah reported, tracing it back to the Prophet ﷺ, "The fitrah is five, or five things are part of the fitrah: circumcision, shaving the pubic hair, plucking the underarm hair, trimming the nails, and clipping the moustache."
حدثنا مسدد حدثنا سفيان عن الزهري عن سعيد
يبلغ به النبي ﷺ الفطرة خمس أو خمس من الفطرة الختان والاستحداد ونتف الإبط وتقليم الأظفار وقص الشارب
Bukhari narrated it in Sahih Bukhari, Book of Dress, Chapter on Trimming the Mustache, no. 5889, and Muslim, Book of Purification, Chapter on the Characteristics of Fitrah, no. 257, from the hadith of Sufyan bin Uyayna, with this same chain.