Abu Dawud Book 34, Hadith Number 4518.
Chapter : If a man finds someone with his wife should he kill him.
Narated By N/A : Abu Hurairah told that Sa’d b. ‘Ubadah said to the Apostle of Allah (may peace be upon him): “What do you think if I find with my wife a man; should I give him some time until I bring four witnesses?” He said: Yes.