When Ibn 'Umar was asked about a man who divorced his wife when she was menstruating, he would say:
If it is the first or second divorce, the Messenger of Allah would tell him to take her back and keep her until she has menstruated again and purified herself, then divorce her before having intercourse with her. But if it was three simultaneous divorces, then you have disobeyed Allah with regard to the way in which divorce should be conducted and your wife has become irrevocably divorced.