Sahih Muslim | Book 30 | Hadith Number 5782

Narrated by Thabit
Thabit reported that Anas b. Malik was asked about the dyeing (of the hair of) Allah's Apostle (may peace be upon him). 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.