A man of Banu al-Ajlan came to Asim bin Adi and said: "O Asim! What do you think of a man who finds a (strange) man with his wife: should he kill him, and then you kill him in retaliation, or what should he do? Ask the Messenger of Allah (peace and blessings be upon him) for me." The Messenger of Allah (peace and blessings be upon him) disliked such questions and found fault with them, so much so that what Asim heard from the Messenger of Allah (peace and blessings be upon him) weighed heavily on him. When Asim returned to his family, Uwaymir came and said: "O Asim! What did the Messenger of Allah (peace and blessings be upon him) say to you?" Asim said: "The Messenger of Allah (peace and blessings be upon him) disliked the question you asked me to put." Uwaymir came forward until he asked the Messenger of Allah (peace and blessings be upon him) in the midst of the people, saying: "O Messenger of Allah! What do you think of a man who finds a (strange) man with his wife: should he kill him, and then you kill him, or what should he do?" He (peace and blessings be upon him) said: "A verse has been revealed concerning you and your companion; go and bring her." Sahl (may Allah be pleased with him) said: So the two of them performed li'an (mutual imprecation), and I was present with the people in the presence of the Messenger of Allah (peace and blessings be upon him). When the two of them had finished their li'an, Uwaymir said: "O Messenger of Allah! If I keep her, I will have lied against her." The narrator said: So he divorced her before the Messenger of Allah (peace and blessings be upon him) ordered him to divorce her, and this separation of his from her became the practice between those who perform li'an.
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 5671