Musnad Ahmad 790:125

Muhammad ibn Abdullah al-Ansari narrated to us, Salih ibn Rustum al-Khazzaz narrated to us, he said: Kathir ibn Shanzir narrated to me, from al-Hasan, from Imran ibn Husayn, who said: The Messenger of Allah (peace and blessings of Allah be upon him) never stood among us to deliver a sermon without commanding us to give charity and forbidding us from mutilation (al-muthlah). He said: And he said: "Beware, and indeed, among the forms of mutilation is that a man vows to pierce his nose."