Musnad Ahmad 937:19

'Abd al-Razzaq narrated to us, Ma'mar informed us, from Sa'id al-Jurayri, from 'Abd Allah ibn Buraydah al-Aslami, from Abu al-Aswad, from Abu Dharr, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, the best thing with which this gray hair is changed is henna and katam."