Musnad Abu Ya'la al-Mawsili 2:81

Zakariya ibn Yahya Zahmuwayh al-Wasiti narrated to us, Umar ibn Harun narrated to us, from Hanzala ibn Abi Sufyan, from Salim ibn Abdullah, from his father, who said: I saw Umar ibn al-Khattab kiss the Stone and prostrate upon it. Then he returned and kissed it and prostrated upon it. Then he said: "This is how I saw the Messenger of Allah, may Allah bless him and grant him peace, do."