Sayyiduna Nu'aym bin Hazzal al-Aslami (may Allah be pleased with him) said that Ma'iz (may Allah be pleased with him) came to the Prophet (peace and blessings be upon him) and said: I have committed adultery, so judge me according to the Book of Allah. He (peace and blessings be upon him) turned away from him, until he had confessed four times; then he (peace and blessings be upon him) said: "Go and stone him." When the stones struck him, he ran because of the pain; then Abdullah bin Unays (may Allah be pleased with him) struck him with a donkey's shank-bone and knocked him down, and the people also pelted him until he died. When his running away was mentioned to the Prophet (peace and blessings be upon him), he (peace and blessings be upon him) said: "Why did you not leave him? Perhaps he would have repented, and Allah would have accepted his repentance. O Hazzal, had you covered him with your garment, that would have been better for you than what you did."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحدود / 16958