Sahih Bukhari , Volume 4, Book 56, Number 814:

Narrated Anas:

There was a Christian who embraced Islam and read Surat-al-Baqara and Al-Imran, and he used to write (the revelations) for the Prophet. Later on he returned to Christianity again and he used to say: “Muhammad knows nothing but what I have written for him.” Then Allah caused him to die, and the people buried him, but in the morning they saw that the earth had thrown his body out. They said, “This is the act of Muhammad and his companions. They dug the grave of our companion and took his body out of it because he had run away from them.” They again dug the grave deeply for him, but in the morning they again saw that the earth had thrown his body out. They said, “This is an act of Muhammad and his companions. They dug the grave of our companion and threw his body outside it, for he had run away from them.” They dug the grave for him as deep as they could, but in the morning they again saw that the earth had thrown his body out. So they believed that what had befallen him was not done by human beings and had to leave him thrown (on the ground).