Musnad Ahmad 32:1865

'Attab narrated to us, 'Abdullah informed us, Al-Muthanna bin Sa'id informed us, from Qatadah, from Anas: "The Prophet, peace and blessings of Allah be upon him, never dyed [his hair]. The whiteness was only in the front of his beard, a little in the lower lip hair (the 'anfaqah), and a small amount on his head, which could hardly be seen." And Al-Muthanna said: "And [in] the temples."