Musnad Abu Ya'la al-Mawsili 2:82

Uthman ibn Abi Shaybah narrated to us, Ibn Idris narrated to us, from Hizam ibn Hisham ibn Hubaysh ibn al-Ashqar al-Khuza'i, who said: I heard my father mentioning that he saw Umar ibn al-Khattab kissing the Stone. And he said: "I bear witness that you are a stone, but I saw the Messenger of Allah, may Allah bless him and grant him peace, kissing you."