Musnad Ahmad 32:848

Mu'ammal and Hasan al-Ashyab narrated to us, they said: Hammad narrated to us, Thabit narrated to us, from Anas—Hasan said: from Thabit and Humayd, from Anas—that the Messenger of Allah (peace and blessings of Allah be upon him) passed by a garden belonging to the Banu al-Najjar on his grey mule. He heard the voices of people being punished in their graves, and the mule shied away. The Prophet (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."