Musnad Abu Ya'la al-Mawsili 3:303

Ubayd Allah narrated to us, Sakan ibn Ibrahim al-Barjami Abu Amr narrated to us, Ash'ath ibn Siwar narrated to us, from Ibn Ashwa', from Hanash al-Kinani, from Ali ibn Abi Talib, that he sent his chief of police and said to him: "Do you know for what I am sending you? I am sending you for what the Messenger of Allah, may Allah bless him and grant him peace, sent me for: that I should efface every decoration"—he said, meaning every image—"and that I should level every grave."