Hadith: ‘Uwaymir al-‘Ajlāni went to ‘Āsim ibn ‘Adyy al-Ansāri and asked: O ‘Āsim, tell me, if a man sees his wife (sleeping) with another man, should he kill him, whereupon you will kill him (in retribution), or what should he do? O ‘Āsim, ask the Messenger of Allah (may Allah’s peace and blessings be upon him) about that

عن ابن شهاب، أن سهل بن سعد الساعدي أخبره: أن عُوَيْمِراً العجلاني جاء إلى عاصم بن عدي الأنصاري، فقال له: يا عاصم، أرأيت رجلاً وجد مع امرأته رجلاً، أيقتله فتقتلونه، أم كيف يفعل؟ سل لي يا عاصم عن ذلك رسول الله صلى الله عليه وسلم ، فسأل عاصم رسول الله صلى الله عليه وسلم عن ذلك، فكره رسول الله صلى الله عليه وسلم المسائل وعابها، حتى كبر على عاصم ما سمع من رسول الله صلى الله عليه وسلم ، فلما رجع عاصم إلى أهله جاءه عويمر، فقال: يا عاصم، ماذا قال لك رسول الله صلى الله عليه وسلم ؟ فقال عاصم لعويمر: لم تأتني بخير، قد كره رسول الله صلى الله عليه وسلم المسألة التي سألته عنها، فقال عويمر: والله لا أنتهي حتى أسأله عنها، فأقبل عويمر حتى جاء رسول الله صلى الله عليه وسلم وسط الناس، فقال: يا رسول الله، أرأيت رجلاً وجد مع امرأته رجلًا، أيقتله فتقتلونه، أم كيف يفعل؟ فقال رسول الله صلى الله عليه وسلم : «قد أُنزِل فيك وفي صاحبتك، فاذهب فَأْتِ بها» قال سهل: فَتَلاعَنا وأنا مع الناس عند رسول الله صلى الله عليه وسلم ، فلما فَرَغَا مِن تَلاعُنِهِما، قال عويمر: كذبت عليها يا رسول الله إنْ أَمْسَكْتُها، فطلقها ثلاثا، قبل أن يأمره رسول الله صلى الله عليه وسلم ، قال ابن شهاب: فكانت سُنَّة المُتلاعِنَيْن.
[صحيح] - [متفق عليه]

Ibn Shihāb reported that Sahl ibn Sa‘d As-Sā‘idi (may Allah be pleased with him) said to him: "‘Uwaymir al-‘Ajlāni went to ‘Āsim ibn ‘Adiyy al-Ansāri and asked: ‘O ‘Āsim, tell me, if a man sees his wife (sleeping) with another man, should he kill him, whereupon you will kill him (in retribution), or what should he do? O ‘Āsim, ask the Messenger of Allah (may Allah’s peace and blessings be upon him) about that.' ‘Āsim asked the Messenger of Allah (may Allah’s peace and blessings be upon him) about that, but the Prophet disliked the question and considered it disgraceful, which upset ‘Āsim. When he returned to his family, ‘Uwaymir went to him and said: ‘O ‘Āsim, what did the Messenger of Allah (may Allah’s peace and blessings be upon him) say to you?’ ‘Āsim replied: ‘You did not bring me any good. The Messenger of Allah (may Allah’s peace and blessings be upon him) disliked the question which I asked him.’ Thereupon, ‘Uwaymir said: ‘By Allah! I will not stop until I ask him about that.’ So, he went to the Messenger of Allah (may Allah’s peace and blessings be upon him) while he was amongst people, and said: ‘O Messenger of Allah, if a man finds another man (sleeping) with his wife, should he kill him, whereupon you will kill him (in retribution), or what should he do?’ The Messenger of Allah (may Allah’s peace and blessings be upon him) said: ‘Something has been revealed concerning you and your wife. So, go and bring her.’” Sahl said: "They both engaged in Li‘ān and I witnessed it along with the people in the Prophet’s presence. When they were done, ‘Uwaymir said: ‘O Messenger of Allah, If I kept her as a wife, It would mean that I fabricated a lie against her then.’ So, he pronounced divorce against her three times before the Messenger of Allah (may Allah’s peace and blessings be upon him) ordered him to do so.'” Ibn Shihāb added: "c2">“So it became a tradition to dissolve the marriage of those spouses who are involved in a case of Li‘ān.”
Sahih/Authentic. - [Al-Bukhari and Muslim]

Explanation

This Hadīth informs us that ‘Uwaymir al-‘Ajlāni (may Allah be pleased with him) asked about the ruling regarding the man who sees another man sleeping with his wife, and what he should do. The Prophet (may Allah's peace and blessings be upon him) disliked to tackle such an issue, given the unpleasant aspects involved therein. ‘Uwaymir, however, insisted on posing this question, which was concerning a matter that had actually happened to him. So, he went to the Prophet (may Allah's peace and blessings be upon him) and asked about the ruling regarding his case. In response, the Prophet (may Allah's peace and blessings be upon him) informed ‘Uwaymir that Allah, the Almighty, revealed Qur’an containing the judgment on their case. Thereupon, he and his wife engaged in Li‘ān. ‘Uwaymir (may Allah be pleased with him) did not know that Li‘ān would automatically make his wife forbidden for him, so he pronounced divorce three times against her. This was the first case of Li‘ān in Islam.