A friend who’s getting married tomorrow wants to put a condition in her nikah contract that her husband won’t marry another wife – is that fine?
Is she allowed to put a condition against something that is Islamically permissible or is it okay because he’s giving up his own rights?
بِسْمِ اللهِ الرَّحْمنِ الرَّحِيْم
In the name of Allah, the Most Gracious, the Most Merciful
It is a usual expectation for most persons that they are overwhelmed with happiness and great anxiety immediately before entering a marriage. Sometimes promises are made by both parties due to being overjoyed which are seldom fulfilled. We are commanded by Allah in the Quran,” Oh you who have believed, fulfill your oaths, verily oaths will be taken into account.” Such oaths refer to the solemn promises made amongst ourselves. However, we are not allowed to change the permissibility or prohibition of any matter in the Deen of Allah regardless of how overjoyed we may be.
The prophet (s.a.w.) has also invalidated the conditions which people impose upon one another which are not found in the book of Allah.
In essence, the allowance of a man having more than one wife is found in the book of Allah. If the husband makes such an oath as not to marry any other woman, then it is preferred that he keeps that oath as far as he can. But if he breaks the oath it will not nullify his marriage. We are advised against taking up burdens which we may not be able to bear. If the oath is broken, then the expiration of the oath will be due from him.
Abu Bakr As-Siddiq had never broken his oaths till Allah revealed the expiation for the oaths. Then he said, "If I take an oath to do something and later on I find something else better than the first one, then I do what is better and make expiation for my oath."
Allah has made our Deen easy for us to practice, even if we make errors he has given us avenues to make up for such mistakes.
Only Allah knows best
Written by Maulana Naieem Mohammad
Checked and approved by Mufti Mohammed Tosir Miah
Darul Ifta Birmingham
 Surah Al Israa,vs 34,Tafseer Ibnu Katheer.
 Saheeh Muslim,book # 9 hadith #3585
 Bukhari 6621,book 83 hadith1