Musnad Ahmad 33:499

Hassan narrated to us, Ibn Lahi'ah narrated to us, Abu al-Zubayr narrated to us, Jabir ibn Abdullah narrated to me: "That the Messenger of Allah, may Allah bless him and grant him peace, commanded Umar ibn al-Khattab at the time of the Conquest to go to the House (the Kaaba) while he was at al-Batha, and to erase every image in it. And he did not enter it until every image in it had been erased."