Musnad Ahmad 32:156

Sufyan narrated to us, he said: Qasim al-Rahhal heard Anas saying: The Prophet, peace and blessings of Allah be upon him, entered a ruin belonging to Banu al-Najjar as if he were relieving himself therein. He came out to us terrified or alarmed, and said: "Were it not that you would not bury one another, I would have asked Allah to let you hear from the punishment of the people of the graves what I hear."