Sahih Bukhari, Chapter: Pilgrimage (Hajj)

from his father who said, "Umar bin Al-Khattab addressed the Corner (Black Stone) saying, 'By Allah! I know that you are a stone and can neither benefit nor harm. Had I not seen the Prophet touching (and kissing) you, I would never have touched (and kissed) you.' Then he kissed it and said, 'There is no reason for us to do Ramal (in Tawaf) except that we wanted to show off before the pagans, and now Allah has destroyed them.' 'Umar added, '(Nevertheless), the Prophet did that and we do not want to leave it (i.e. Ramal).'