Musnad Ahmad 32:1320

Abu Sa’id narrated to us, Al-Muthanna narrated to us, from Qatadah, from Anas: "The Messenger of Allah (peace and blessings of Allah be upon him) never dyed his hair. The whiteness was only in the front of his beard, in the tuft of hair below the lower lip (al-‘unfuqah), on his head, and on his temples, [in] a small amount that could hardly be seen." And Abu Bakr dyed [his hair] with henna.