Is it permissible for a woman to remain with her former husband, who took her back after a divorce without her knowledge or the knowledge of her family and before the iddah (waiting period) ended, and what is the expiation for this act for the husband, the wife, and the third party? And if his action was legitimate, is it permissible for the woman to seek khul' (divorce at her initiative) from him due to her refusal to continue with him?

The husband of a woman divorced revocably has the right to take her back as long as her waiting period (iddah) has not expired, based on the Almighty's saying: "And their husbands have a greater right to take them back during this period, if they wish reconciliation." So, if the divorced husband proves his reconciliation with his wife before the expiration of her iddah with just evidence, then he has a greater right to her. The wife's knowledge is not a condition for the validity of the reconciliation. The decision in this matter rests with the Sharia courts. If his reconciliation is proven, then the woman and her husband are considered spouses according to Islamic law, and she must repent for the poor relationship. There is no expiation other than repentance. As for the questioner maintaining a relationship with that girl after her return to her husband, this is wrong because she is a married woman. The Messenger of Allah, peace and blessings be upon him, said: "He is not from us who instigates a woman against her husband." This girl has the right to seek a khul' (divorce initiated by the wife) from her husband if she dislikes him.