Musnad Ahmad 2:148

Abu Mu'awiyah narrated to us, 'Asim al-Ahwal narrated to us, from 'Abdullah ibn Sarjis, who said: I saw the one with the small bald spot—meaning 'Umar—kissing the Stone and saying: "Verily, I am kissing you, and I know that you are a stone that neither benefits nor harms. And were it not that I saw the Messenger of Allah, may Allah bless him and grant him peace, kissing you, I would not have kissed you."