Abu Dawud Book 28, Hadith Number 4188.
Chapter : Clipping the moustaches.
Narated By Anas b. Malik : The Apostle of Allah (PBUH) fixed forty days to shave the pubes, paring the nails, clipping the moustaches, and plucking the hair under the armpit.
Abu Dawud said: Js’far b. Sulaiman transmitted it from Abu Imran on the authority of Anas. In this version he did not mention the Prophet (PBUH). He said: Forty days were fixed for us. This is a more correct version.