Musnad Ahmad 32:2087

'Affan narrated to us, Hammad narrated to us, he said: Thabit and Humayd informed us, from Anas, that the Messenger of Allah (peace and blessings of Allah be upon him) passed by a graveyard of the Banu al-Najjar in an orchard, while he was upon a grey mule. Suddenly, he was at a grave where [someone] was being punished, so the mule shied away. The Messenger of Allah (peace and blessings of Allah be upon him) said: "Were it not that you would not bury one another, I would have asked Allah to let you hear the punishment of the grave."