Musnad Ahmad 1238:3

Muhammad ibn Abdullah ibn al-Zubayr narrated to us, he said: Isra'il narrated to us, from Simak, from Alqama ibn Wa'il, from his father, who said: A woman went out for prayer, and a man met her, covered her with his garments, satisfied his need with her, and left. Then a man came upon her, and she said to him: "A man did such and such to me." So the man went in pursuit of him. Then a group of the Ansar came upon her and stopped by her. She said to them: "A man did such and such to me." So they went in pursuit of him, and they brought the man who had gone in pursuit of the man who had violated her. They took him to the Prophet, peace and blessings of Allah be upon him, and she said: "It is this one." When the Prophet, peace and blessings of Allah be upon him, ordered his stoning, the one who had violated her said: "O Messenger of Allah, by Allah, I am the one." He said to the woman: "Go, for Allah has forgiven you." He said a good word to the man. It was said: "O Prophet of Allah, will you not stone him?" He replied: "He has repented with a repentance that, if the people of Medina had repented it, it would have been accepted from them."