Narrated 'Abis bin Rabia: 'Umar came near the Black Stone and kissed it and said "No doubt, I know that you are a stone and can neither benefit anyone nor harm anyone. Had I not seen Allah's Apostle kissing (and sexual intercourse with) you I would not have kissed you."(Sahih Al Bukhari:Vol. 2:Bk.26:No.667)