Amr b. Shu’aib (RA), on his father’s authority, told that his grandfather reported the Messenger of Allah (SAW) said: Do not pluck out grey hair. If any believer grows a grey hair in Islam, he will have light on the Day of Resurrection. (This is Sufyan’s version). Yahya’s version says: Allah will record on his behalf a good deed for it, and will blot out a sin for it.
Sunan Abu Dawud Book 34, Hadith 4190