Musnad Ahmad 1017:8

Abu Nu'aym narrated to us, Bashir ibn al-Muhajir narrated to us, 'Abdullah ibn Buraydah narrated to me, from his father, who said: I was sitting with the Prophet, may Allah bless him and grant him peace, when a man called Ma'iz ibn Malik came to him and said: "O Prophet of Allah, I have committed adultery and I want you to purify me." The Prophet, may Allah bless him and grant him peace, said to him: "Go back." When the next day came, he came to him again and confessed adultery before him. The Prophet, may Allah bless him and grant him peace, said to him: "Go back." Then the Prophet, may Allah bless him and grant him peace, sent for his people and asked them about him. He said to them: "What do you know of Ma'iz ibn Malik al-Aslami? Do you see any harm in him, or do you find anything amiss with his intellect?" They said: "O Prophet of Allah, we do not see any harm in him, and we do not find anything amiss with his intellect." Then he returned to the Prophet, may Allah bless him and grant him peace, a third time and confessed adultery before him again. He said: "O Prophet of Allah, purify me." The Prophet, may Allah bless him and grant him peace, sent for his people again and asked them about him. They said to him as they had said the first time: "We do not see any harm in him, and we do not find anything amiss with his intellect." Then he returned to the Prophet, may Allah bless him and grant him peace, a fourth time and confessed adultery before him. The Prophet, may Allah bless him and grant him peace, gave orders, so a pit was dug for him, and he was placed in it up to his chest. Then he ordered the people to stone him. Buraydah said: We, the companions of the Prophet, may Allah bless him and grant him peace, used to say among ourselves: If Ma'iz ibn Malik had stayed in his dwelling after his confession three times, he would not have been sought out; he only stoned him at the fourth time.