Musnad Ahmad 1132:5

Mu'awiyah ibn 'Amr narrated to us, 'Abdullah ibn Wahb narrated to us, from 'Amr—meaning Ibn al-Harith—from Sa'id ibn Abi Hilal, from Abu Bakr ibn Hazm, that an-Nadr ibn 'Abdullah informed him, from 'Amr ibn Hazm, that he heard the Messenger of Allah, peace and blessings of Allah be upon him, say: "Do not sit upon the graves."