سنن النسائي

It was narrated from Sahl bin Sa'd, from 'Asim bin 'Adiyy who said: "Uwaimir, a man from Banu 'Ajlan, came and said: 'O 'Asim, what do you think if a man sees another man with his wife, should he kill him and be killed in retaliation, or what should he do? O 'Asim, ask the Messenger of Allah (ﷺ) about that for me.'" So 'Asim asked the Messenger of Allah (ﷺ) about that, and the Messenger of Allah (ﷺ) disapproved of the question and criticized the asking of too many questions. Then 'Uwaimir came to him and said: "What happened, O 'Asim?" 'Asim said to 'Uwaimir: "What happened?! You have not brought me any good. The Messenger of Allah (ﷺ) disapproved of the question I asked." 'Uwaimir said: "By Allah, I will go and ask the Messenger of Allah." So he went to the Messenger of Allah (ﷺ) and asked him. The Messenger of Allah (ﷺ) said: "Allah the Mighty and Sublime has revealed (something) concerning you and your wife, so bring her here." Sahl said: "I was among the people in the presence of the Messenger of Allah (ﷺ) and he brought her and they engaged in the procedure of Li'an. He said: 'O Messenger of Allah, by Allah! If I keep her I would have been telling lies about her.' So he parted from her before the Messenger of Allah (ﷺ) told him to separate from her, and that became the way of Li'an."