It was narrated that Sahl bin Sa'd As-Sa'idi said:
"Uwaimir came to 'Asim bin 'Adi and said: 'Ask the Messenger of Ailah (ﷺ) for me: "Do you think that if a man finds another man with his wife and kills him, he should be killed in retaliation, or what should he do?" 'Asim asked the Messenger of Allah (ﷺ) about that, and the Messenger of Allah (ﷺ) disapproved of the question. Then 'Uwaimir met him ('Asim) and asked him about that, saying: 'What did you do?' He said: I did that and you have not brought me any good. I asked the Messenger of Allah (ﷺ) and he disapproved of this question.' Uwaimir said: 'By Allah, I will go to the Messenger of Allah (ﷺ) myself and ask him.' So he went to the Messenger of Allah (ﷺ) and found that Qur'an had been revealed concerning them, and the Prophet (ﷺ) told them to go through the procedure of Li'an. 'Uwaimir said: 'O Messenger of Allah, (ﷺ) by Allah if I take her back, I would have been telling lies about her.' So he left her before the Messenger of Allah (ﷺ) told him to do so, and that became the Sunnah for two who engage in the procedure of Li'an. Then the Prophet (ﷺ) said: 'Wait and see. If she gives birth to a child who is black in color with widely-spaced dark eyes and large buttocks, then I think that he was telling the truth about her, but if she gives birth to a child with a red complexion like a Wahrah,[1] then I think that he was lying.' Then she gave birth to a child with features resembling those of the man concerning whom she was accused."
English reference: Vol. 3, Book 10, Hadith 2066
Arabic reference: Book 10, Hadith 2144