Maliks Muwatta Book 54, Hadith Number 5.

Section : Blessing the Person who Sneezes.

Malik related to me from Nafi that when Abdullah ibn Umar sneezed and someone said to him, “May Allah have mercy on you,” (Yarhamuka’llah), he said, “May Allah have mercy on us and you, and forgive us and you.” (Yarhamuna’llah wa yaghfirlana wa lakum).