Musnad Abu Ya'la al-Mawsili 114:8

Al-Hasan ibn Ahmad ibn Abi Shu'ayb al-Harrani narrated to us, Muhammad ibn Salamah narrated to us, Hisham narrated to us, from Ibn Sirin, who said: Anas was asked about the hair dye of the Messenger of Allah, may Allah bless him and grant him peace. He said: "The Messenger of Allah, may Allah bless him and grant him peace, did not have gray hair except for a little, but Abu Bakr and Umar dyed [their hair] with henna and katam." He said: Abu Bakr brought his father, Abu Quhafah, to the Messenger of Allah, may Allah bless him and grant him peace, on the day of the conquest of Makkah. The Messenger of Allah, may Allah bless him and grant him peace, said to Abu Bakr: "Had you left the old man in his house, we would have come to him," out of honor for Abu Bakr. He said: So he accepted Islam, and his beard and head were like the *thaghamah* (a white plant). He said: The Messenger of Allah, may Allah bless him and grant him peace, said: "Change this, and keep him away from black."