´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."
Hadith Referenceسنن نسائي / ذكر الفطرة / 14
Hadith Gradingالألبانی:صحيح | زبیر علی زئی:صحيح مسلم