Muhammad bin Muslim bin Tadras محمد بن مسلم بن تدرس أبو الزبير · Combing the Hair (Kitab Al-Tarajjul)

The Messenger of Allah (ﷺ) fixed forty days to shave the pubes, paring the nails, clipping the moustaches, and plucking the hair under the armpit. Abu Dawud said: Ja'far b. Sulaiman transmitted it from Abu 'Imran on the authority of Anas. In this version he did not mention the Prophet (ﷺ). He said: Forty days were fixed for us. This is a more correct version.

The Prophet (ﷺ) as saying: Jews and Christians do not dye (their beards), so act differently from them.