Sunan Ibn Majah, Chapter: The Chapters on Legal Punishments

"Maiz bin Malik came to the Prophet (saw) and said: 'I have committed fornication,' and he (the Prophet [saw]) turned away from him. He said: 'I have committed fornication,' and he turned away from him. Then, he said: I have committed fornication, and he turned away from him, until when he had confessed four times, he ordered that he should be stoned. When he was being struck with the stones, he ran away, but a man caught up with him who had a camel's jawbone in his hand; he struck him and he fell down. The Prophet (saw) was told about how he fled when the stones hit him and he said: 'Why did you not let him be?'" Hasan