In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
You are not obligated to accept a polygamous marriage. You have the right to choose to be married to a monogamous man. In Islam, monogamy is the ideal and polygamy is an exception.
Responding to your question, Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states:
We read in the Quran:
“If you fear you cannot do justice to the orphans, then marry the women (widows with orphans) as you choose two or three, but if you fear you cannot do justice, then only one.” (An-Nisa’ 4:3)
It is clear from the above verse that the permission to marry more than one was in the context of widows with children whose fathers had been martyred, so it was a social problem and the practical solution was to provide a home for these children where they will enjoy a fatherly figure as well as their mothers.
Moreover, the qualification, if you fear you cannot do justice (to the women you marry), then you are not allowed to marry more than one.
Accordingly, Imam Muhammad Abduh inferred that in Islam monogamy is the ideal and that polygamy is an exception allowed only in exceptional cases.
So, since you have a prenuptial agreement that you would not allow your husband to take a second wife, he is bound by the terms of the contract. The Prophet (peace be upon him) said, “Of all the contractual obligations, the terms of the marriage contract are of greater priority than others.” (Al-Bukhari)
By signing such a contract, you are not in any way displeasing Allah by violating His commandments.
I pray to Allah to make us all steadfast on the straight path.
Almighty Allah knows best.
Source: Ask the Scholar