The rights of the wife if she knows that her husband married another woman

• In Islam the (old) wife has the right to know of the new marriage
• The woman can put a condition in the marriage contract that her husband would not marry another woman, so if he did then the contract can easily be cancelled if she requires that and she can be divorced (and will have all the rights of the divorced woman)
• The (old) wife has the right to ask for a divorce if she refuses that her husband marries another woman. She can not stop him from marrying another but she sure has the right to ask for a divorce.

There is a famous hadith (saying of the Prophet, peace and blessings be upon him) in Al-Bukhari where prophet Muhammad, peace and blessings be upon him, refused that Ali Ibn Abi Talib, may Allah be pleased with him, would marry another woman beside Fatima, may Allah be please with her, the daughter of Prophet Muhammad, peace and blessings be upon him.

The Prophet, peace and blessings of Allah be upon him, said :"I will not allow Ali Ibn Abi Talib and I repeat I will not allow Ali to marry another woman except if he divorces my daughter. She is part of me and what harms her harms me" (Al-Bukhari, al-Jami' al-Sahih, p 453, book 67, chapter 109).

So the noble Prophet, peace and blessings be upon him, did not deny Ali’s right to marry another woman but he told him that he would have to divorce his daughter first. Of course Ali, may Allah be pleased with him, chose the Prophet’s daughter and did not even consider marrying another woman as long as Fatima, may Allah be pleased with her, was alive.

In Islam there is no distinction no nobility over commoners, no black over white, no rich over poor. Prophet Muhammad, peace and blessings be upon him said : “Verily the people before you were destroyed because they would dismiss the punishment of noble person who stole, and if a weak person stole, they would carry out the punishment. I swear by Allah, if Fatimah, daughter of Muhammad stole, I would have cut her hand”.

Precious as she is to her father, Fatimah the daughter of the noble Prophet Muhammad, peace and blessings be upon him, the rules of Islam were applied without discrimination between Muslims. From that story we can conclude that it is the right of the woman to ask for a divorce if she knew that her husband intends to marry another woman.