Sayyiduna Abu Hurayrah (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) said: "Five things are part of the fitrah (natural disposition): circumcision, shaving the pubic hair, trimming the moustache, clipping the nails, and plucking the armpit hair."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجمعة / 5963