Sayyiduna Anas bin Malik (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings be upon him) "set a time limit of forty days for us for shaving the pubic hair, trimming the moustache, clipping the nails and plucking the armpit hair."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 692