Musnad Ahmad 907:61

Bahz narrated to us, Hammad ibn Salamah narrated to us, from Simak, from Jabir ibn Samurah, who said: "There were no gray hairs 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, the oil would conceal them."