A man of the Ansar came to the Prophet (peace and blessings be upon him) and said: O Messenger of Allah, what is your view about a man who finds another man with his wife: if he kills him, will you kill him in retaliation, or what should he do? Thereupon Allah, the Mighty and Majestic, revealed concerning him the verses mentioned in the Qur'an regarding the matter of the two who invoke curses on each other (li'an). The Messenger of Allah (peace and blessings be upon him) said to him: "Allah has given His judgement concerning you and your wife." The narrator (Sahl, may Allah be pleased with him) says: So the two of them performed li'an in the mosque, and I was a witness to it. When they had finished, he said: O Messenger of Allah, if I keep her, then I will have lied against her. So as soon as they finished the li'an, before the Prophet (peace and blessings be upon him) had commanded him, he divorced her three times, and separated from her in the presence of the Prophet (peace and blessings be upon him). The Prophet (peace and blessings be upon him) said: "This is the separation between every couple who perform li'an." And the Prophet (peace and blessings be upon him) said: "If she gives birth to a reddish, short child, as though he were a gecko, then I think that the woman spoke the truth and the man lied against her; and if she gives birth to a black, large-eyed child with big buttocks, then I think that the man spoke the truth about her." And she gave birth to him in the disliked form.
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 5653