Sahih Bukhari
Pilgrimmage (Hajj)
Volume: 002 / Book Number: 026 / Hadith Number: 679
Narrated Zaid bin Aslam that his father said:
"I saw 'Umar bin Al-Khattab kissing the Black Stone and he then said, (to it) 'Had I not seen Allah's Apostle kissing you, (stone) I would not have kissed you.' "