Musnad Ahmad 30:143

Sufyan narrated to us, from al-Zuhri, from Sa’id, from Abu Hurairah, that the Messenger of Allah (may Allah bless him and grant him peace)—and Sufyan said once: "a narration"—said: "Five are of the *fitrah* (natural disposition): circumcision, shaving the pubic hair, trimming the mustache, clipping the nails, and plucking the hair of the armpits."