Pilgrimmage (Hajj)
Bukhari :: Book 2 :: Volume 26 :: Hadith 667
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 you I would not have kissed you."