Sahih Muslim Book 30, Hadith Number 5789.
Chapter : Pertaining to the old age of Allah’s Apostle (may peace be upon him).
Jabir b. Samura reported that there had appeared some whiteness on the front part of the head and beard of Allah’s Messenger (may peace be upon him).When he applied oil, it did not become visible, but when he did not (apply) oil, it became apparent. And he had a thick beard. A person said: His face was as (bright) as the sword. Thereupon he (Jabir) said: No, it was round and like the sun and the moon. And I saw the seal near his shoulder of the size of a pigeon’s egg and its colour was the same as that of his body.