Sahih Muslim Book 7, Hadith Number 2913.

Chapter : Excellence of kissing the black stone ;while circumambulating.

Ibn ‘Umar (Allah be pleased with them) reported that Umar (Allah be pleased with him) kissed the Stone and said: I am kissing you, whereas I know that you are a stone, but I saw Allah’s Messenger (may peace be upon him) kissing you (that Is why I kiss you).