Musnad Ahmad 907:182

'Abd al-Rahman ibn Mahdi narrated to us, from Hammad ibn Salamah, from Simak ibn Harb, from Jabir ibn Samurah, who said: "There was nothing of gray hair on the head of the Messenger of Allah, peace and blessings of Allah be upon him, except for a few hairs at the parting of his head. When he applied oil, he would cover them."