Sahih Muslim 6076
صحيح مسلم#6076SahihThabit reported that Anas b. Malik was asked about the dyeing (of the hair of) Allah's Apostle (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
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih Muslim is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 43:134