صحيح مسلم

Thabit reported that Anas b. Malik was asked about the dyeing (of the hair of) Allah's Messenger (ﷺ). Thereupon he said.: (They were so few) that if I so liked I could count their number in his head, and he further said: (That is) he did not dye. Abu Bakr, however, dyed them and so did 'Umar dye them with pure henna.