As-salamu `alaykum. What should a man do if he finds his wife making love to another man? Can he kill both of them?And the answer:
Of course, he can not kill them, but he has every right to divorce her.You have to wonder if this was a practical or a theoretical question.
In areas where Islamic Law is applied, he may do li`an (oath of condemnation). Due to the absence of four witnesses, he may swear before the judge that he saw her committing adultery and that Allah’s curse would be upon the liar, and she would also have the right to swear the same way.
After that the couple are separated and they cannot be husband and wife again. In the absence of li`an, the husband can simply divorce his wife if he found her in such a situation, and if he wants he has the right to take her to court as well.