Nafi' narrates from Abdullah bin Umar (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "These acts are part of the fitrah (natural disposition): trimming the moustache, clipping the nails, and shaving the pubic hair."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجمعة / 5962