Musnad Ahmad 1014:1

Zayd ibn al-Hubab narrated to us, Husayn narrated to us, Abu Nahik narrated to me, Abu Zayd ‘Amr ibn Akhtab al-Ansari narrated to me, he said: The Messenger of Allah (may Allah bless him and grant him peace) asked for water, so I brought him a cup containing water, and there was a hair in it. I took it out, and he said: "O Allah, beautify him." He said: I saw him when he was ninety-four years old, and there was not a single white hair in his beard.