Musnad Ahmad 32:611

Hassan—meaning Ibn Musa—narrated to us, Hammad ibn Salamah narrated to us, from Thabit and Humayd, from Anas, that the Messenger of Allah (peace and blessings of Allah be upon him) was upon a grey mule. He passed by a garden belonging to the Banu al-Najjar, and there he was at a grave whose occupant was being punished. The mule shied away. He said: "Were it not that you would not bury one another, I would have supplicated to Allah to let you hear the punishment of the grave."