Musnad Ahmad 5:500

Waki’ and ‘Abd al-Rahman narrated to us, from Sufyan, from Habib, from Abu Wa’il, from Abu al-Hayyaj, who said: Ali said to me—‘Abd al-Rahman said: Indeed, Ali said to Abu al-Hayyaj: "Shall I not send you on that which the Messenger of Allah (peace and blessings of Allah be upon him) sent me? That you shall not leave any raised grave without leveling it, nor any image without effacing it."