What is the ruling on one who divorces his wife while she is menstruating, knowing that the divorce takes effect, then takes her back after the 'iddah has ended, knowing that she can be taken back in this situation? And does his wife count as having returned to his marital authority, knowing that the divorce certificate has not been issued?

Divorcing a menstruating woman is forbidden, yet valid, according to the majority of scholars. If a man divorces his wife while she is menstruating, and her 'iddah (waiting period) has elapsed, then she is irrevocably divorced from him. Reconciling with her after the 'iddah is not permissible. Any conjugal relations between them after they have become aware of this ruling are considered zina (adultery), and he must separate from her. If he wishes to return to her and he divorced her less than three times, there is no impediment to him marrying her again with a new contract, provided all conditions and pillars are fulfilled.