The World Federation One Stop Fiqh

Ruling 2519

If a man knows his wife to be clear of ḥayḍ and divorces her but later realises that she was in the state of ḥayḍ  at the time of the divorce, the divorce is void except in the scenario mentioned above]. If he knows her to be in the state of ḥayḍ but divorces her nonetheless and it later becomes known that she was not in the state of ḥayḍ, the divorce is valid.