It was narrated that Anas bin Malik said:
"A time limit was set for us, by the Messenger of Allah (ﷺ), regarding trimming the mustache, clipping the nails and plucking the pubes; we were not to leave that for more than forty days," on one occasion he said: "Forty nights."
Arabic/English book reference: Vol. 1, Book 1, Hadith 14