Hazrat Mak'hool (may Allah have mercy on him) said: If a man, after giving two divorces, accuses his wife of adultery, then if he declares himself to be a liar, the prescribed punishment (hadd) will be carried out on him and he may, if he wishes, take her back. But if he does not declare himself to be a liar, then they will perform li'an (mutual cursing) and there will be a permanent separation between them.
Hadith Referenceسنن سعید بن منصور / كتاب الطلاق / 2773