Musnad Ahmad 2:95

Abu Mu'awiyah narrated to us, he said: Al-A'mash narrated to us, from Ibrahim, from 'Abis ibn Rabi'ah, who said: I saw 'Umar kissing the Stone, and he said: "Verily, I am kissing you, and I know that you are a stone. 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."