Musnad Abu Ya'la al-Mawsili 2:78

Abu Khaythama narrated to us, Hushaym narrated to us, Ibn Abi Layla narrated to us, from ‘Ata’, from Ya‘la ibn Umayyah, who said: I saw ‘Umar ibn al-Khattab touch the Black Stone and kiss it. He said: "Verily, I am kissing you, and I know that you are a stone that neither harms nor benefits, but I saw the Messenger of Allah (may Allah bless him and grant him peace) kiss you."