First of all, every Muslim has to keep in mind the fact that divorce is the most hated permissible thing in the sight of Allah. It dissolves families and deprives children the family atmosphere. The Prophet, peace and blessings be upon him, said: “The most hateful permissible thing (al-Halal) in the sight of Allah is divorce.” (Abu Dawud, Hadith 1863, and Ibn Majah, Hadith 2008).
The spouses should avoid divorce as much as possible. If they have difficulties and problems they should be patient and forbearing. They have to try to work out their differences and seek help from their relatives, friends or professional counselors.
Dr. Muzammil H. Siddiqi, former President of the Islamic Society of North America, states: “According to the Qur’an and Sunnah, a man is allowed to have more than one wife (up to four) with the strict condition that he will treat all of them with equity. Multiple marriages are only a permission, and they could be good and useful for some people and in some situations. However all those who opt to have more than one wife, they must treat them all with love, kindness and equity. If a woman in a multiple marriage situation finds herself mistreated or treated unjustly, she has a right to seek divorce from her husband.
It is also permissible for a woman to make this as a condition of marriage that her husband will not take another wife during his marriage to her. This pre-condition is permissible according to most jurists. If a husband accepts this pre-condition then he has to abide by it. In case he fails, the wife has a right to seek divorce according to her contract of marriage.”
Moreover, the eminent Muslim scholar, Sheikh Muhammad Salih Al-Munajjid, points out:
“Concerning the first wife’s request for divorce if her husband wants to marry another wife, this is a mistake. But they should examine the situation, and if she really cannot cope with living with another wife, then she can ask him for Khul`. If she can cope with living with the second wife, but it hurts her to do so, then she should be patient and seek the pleasure of Allah. Thawban (may Allah be pleased with him) narrated that the Messenger of Allah (peace and blessings be upon him) said: “No woman asks her husband for a divorce for no reason, but the fragrance of Paradise is forbidden for her.” (Reported by Abu Dawud and others)
If she bears it with patience, then Allah will make it easier for her and will expand her chest (i.e. grant her peace and calm) and will compensate her with something good. The husband must also help her by treating her kindly, being patient with her for any jealousy etc. on her part, and overlooking her mistakes.”
It is clear that, as a wife one should not ask for a divorce as soon as her husband announces he wants to marry a second wife. If he has gone ahead with the second marriage, do your best to continue to make your marriage happy and do not create problems between him and his second wife. If you act sullenly or angrily with him, he might well divorce you.
But do you really want to live alone without any husband, especially if you have children? I have seen sisters who were co-wives who got along well with each other and were happy in their marriages. Make the effort, with the help of Allah, to bear the situation. Only if he is really treating you unjustly—not spending alternate days and nights with you, not spending equally on you, etc.—should you ask for a divorce.
If he has not yet married the second one but has only voiced his intention, you could calmly ask him to delay the decision for two or three months. He may change his mind after considering his situation, but if you react with anger he may go ahead and marry the second one immediately to get back at you.
During that interval, ask yourself if there is anything wrong with your marriage that would make him want to take a second wife. Sometimes when men say they want another wife, they really mean that they have a problem with the first. They might then take a second wife with the thought that that will make the problem better. If you find that the two of you need to work to improve your own marriage, then seek the advice of family, pious friends, or professional counsellors.
And he might not change his mind but go ahead with the second marriage. Then, its adviced is as before: pray for patience and make an effort to make your marriage happy.