Musnad Abu Ya'la al-Mawsili 108:52

Abu Bakr narrated to us, Sharik narrated to us, from al-Ajlah, from Abu al-Zubayr, from Jabir, who said: When the Prophet, peace and blessings of Allah be upon him, arrived in Makkah, Abu Quhafah was brought to him, and his head and beard were as if they were *thughamah* (a white plant). He said: "Change the gray hair, and avoid black."