According to many scholars including Ḥanbalīs, a woman has the right of stipulating at the marriage contract that her husband should not get married to a second or  a third wife.

In case the husband does not fulfil this condition, the contract will be null and void. This view is held by `Umar ibn Al-Khattab, Sa`d ibn Abi Waqqas, Mu`awiyah, `Amr ibn Al-`Aas, `Umar ibn `Abd Al-`Aziz, Jabir ibn Zayd, Tawus, Al-Awza`i, Is-haq, and the Hanbali jurists. They quote the following proofs in support of their opinion:

– Allah Almighty says, “O ye who believe! Fulfill your undertakings.” (Al-Maidah 5:1)

Al-Bukhari, Muslim and others reported on the authority of `Uqbah ibn `Amir that Allah’s Messenger (peace and blessings be upon him) is reported to have said, “The conditions you have the most duty to fulfill are those by which you have made marital relations lawful.”

With his chain of narrators, Al-Athram reported that a man married a woman; it was stipulated in the marriage contract that he should provide her a certain house. Thereafter, the husband wanted her to dwell in another house, so the wife lodged a complaint to `Umar ibn Al-Khattab; `Umar said that the wife should be provided with the house stipulated in the marriage contract.

They, moreover, maintain that the wife’s condition that her husband should not marry another beside her, is binding, for it contains a benefit for the wife and does not contradict the objectives of marriage; it is the same as the stipulation of increasing the dower.

Ibn Qudamah gives preference to this view over the first; he says, “This was the opinion of the Companions, and we do not know anyone who disagreed with them in their lifetime.

In addition, the hadith that states: “Any condition which has no basis in the Book of Allah is void” means any condition which is inconsistent with the rules of Shari`ah, but such a condition is admissible, and we have mentioned the proofs that support its admission; therefore, he who doubts its admission should support his view with evidences.”

Other scholars maintain that the contract of marriage is valid, but the accompanying conditions are void, so the husband is not bound to fulfil these conditions. This is the view of Abu Hanifah, Ash-Shafi`i, and many other jurists.

They based their view on the report of the Prophet (peace be upon him) in which he said, “Muslims are bound by their conditions, unless it be a condition which turns a lawful act into haram or a haram into halal.”

They maintain that the wife’s stipulating that her husband must not marry another beside her, or not to take her with him in his journeys, is null and void, because it makes a lawful thing, i. e. marriage or accompanying her in travels, unlawful.

Based on the above fatwa, the wife has the right to stipulate in the marriage contract that her husband must not marry another beside her and it’ll be binding upon him. If the man marries another wife, then she is given the choice either to claim for divorce or to stay with him as a co-wife.

Almighty Allah knows best.