Is it permissible for a Muslim woman to ask a man who is married to a non-Muslim woman to be his only wife, knowing of his desire to marry a Muslim woman like her and his claim that she is not the reason for the divorce?

If the man is pleasing in his religious commitment and character, then he may be accepted. However, stipulating that he divorce his disbelieving wife is not appropriate, as it involves injustice towards her and an aggression against her rights, due to the Prophet’s (peace and blessings of Allah be upon him) saying: “It is not permissible for a woman to ask for the divorce of her sister so that she may empty her plate, for she will only have what has been decreed for her.” The meaning of “her sister” includes her co-wife, whether Muslim or disbelieving. The hadith indicates submission to divine decree and that provision is predetermined. It is safer to refrain from stipulating divorce, out of faith in divine decree.