Musannaf Ibn Abi Shayba 16:771

Abu Bakr narrated to us, he said: Ibn Idris narrated to us, from al-Ajlah, from Abdullah ibn Buraydah, from Abu al-Aswad al-Du'ali, from Abu Dharr, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, the best thing with which you change gray hair is henna and katm."