Question 1: A Christian woman who is married to a Christian man has embraced Islaam but he has not accepted Islaam yet. They are old now and no longer have sexual intercourse; is it permissible for her to remain with him or should the marriage contract be cancelled? How long should her `Iddah (woman’s prescribed waiting period after divorce or widowhood) be? What is the ruling on the Mahr (mandatory gift to a bride from her groom)? Is it permissible for him to take her back if he embraces Islaam?
Answer: If a Christian woman embraces Islaam while married to a Christian man, the marriage contract becomes invalid, and she is to give back the Mahr she received. Allaah (Exalted be He) states: …then if you ascertain that they are true believers send them not back to the disbelievers. They are not lawful (wives) for the disbelievers nor are the disbelievers lawful (husbands) for them. But give them (the disbelievers) that (amount of money) which they have spent [as their Mahr] to them.... read more here.