Abu Dawud Book 28, Hadith Number 4190.
Chapter : Plucking out grey hair.
Narated By Abdullah ibn Amr ibn al-‘As : The Apostle of Allah (PBUH) 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.