Musnad Ahmad 32:1380

Hashim narrated to us, Sulayman narrated to us, from Thabit, from Anas ibn Malik, who said: "There was a man among us from Banu al-Najjar who had recited [the surahs of] al-Baqarah and Ali 'Imran, and he used to write for the Messenger of Allah, may Allah bless him and grant him peace. Then he fled, escaping until he joined the People of the Book. They raised him up and said, 'This man used to write for Muhammad,' and they were impressed by him. But it was not long before Allah broke his neck among them. So they dug for him and buried him, but by morning, the earth had cast him out onto its surface. Then they returned and dug for him and buried him, but by morning, the earth had cast him out onto its surface. Then they returned and dug for him and buried him, but by morning, the earth had cast him out onto its surface. So they left him cast out."