The importance of marriage contract in Islam

قال الشيخ صالح الفوزان حفظه الله :

"من الشروط الصحيحة في النكاح : إذا شرطت عليه أن لا يتسرى ، أو لا يتزوج عليها ، فإن وفّى ، وإلا فلها الفسخ ؛ لحديث : (أَحَقُّ الشُّرُوطِ أَنْ تُوفُوا بِهِ مَا اسْتَحْلَلْتُمْ بِهِ الْفُرُوجَ) وكذا لو شرطت أن لا يفرق بينها وبين أولادها أو أبويها ؛ صح هذا الشرط ، فإن خالفه ؛ فلها الفسخ . ولو اشترطت زيادة في مهرها ، أو كونه من نقد معين ؛ صح الشرط ، وكان لازما ، ويجب عليه الوفاء به ، ولها الفسخ بعدمه ، وخيارها في ذلك على التراخي ، فتفسخ متى شاءت ؛ ما لم يوجد منها ما يدل على رضاها مع علمها بمخالفته لما شرطته عليه ؛ فحينئذ يسقط خيارها .

قال عمر بن الخطاب رضي الله عنه للذي قضى عليه بلزوم ما شرطته عليه زوجته فقال الرجل  إذاً يطلقننا . فقال عمر : مقاطع الحقوق عند الشروط . ولحديث : (الْمُؤْمِنُونَ عَلَى شُرُوطهمْ) قال العلامة ابن القيم : "يجب الوفاء بهذه الشروط التي هي أحق أن يوفيها ، وهو مقتضى الشرع والعقل والقياس الصحيح ؛ فإن المرأة لم ترض ببذل بضعها للزوج إلا على هذا الشرط ، ولو لم يجب الوفاء به ؛ لم يكن العقد عن تراض ، وكان إلزاماً بما لم يلزمها الله به ورسوله" انتهى .

"الملخص الفقهي" (2/345 ، 346) .

Shaykh Saalih al-Fawzaan (may Allah preserve him) said: 

Among other conditions that are valid in marriage is if she stipulates that he should not take another wife. If he fulfils the condition (all well and good), otherwise she has the right to annul the marriage because of the hadeeth, “The condition which most deserves to be fulfilled is that by means of which intimacy becomes permissible for you.” Similarly, if she stipulates that he should not separate her from her children or parents, this condition is valid and if he breaks it, she has the right to annul the marriage. If she stipulates that her mahr should be increased or that it should be in a specific currency, the condition is valid and binding, and he has to fulfil it, and she has the right of annulment if it is broken. In that case she has the choice and may decide any time she wants and may annul it whenever she wants, so long as there is nothing on her part to indicate that she accepts it if she knows that he has gone against what was stipulated; in that case she would no longer have the option. 

‘Umar ibn al-Khattaab (may Allah be pleased with him) said to the one who he ruled was obliged to fulfil what his wife had stipulated, when the man said, “Divorce us in that case,” ‘Umar said: It is a must to fulfil the conditions, because of the hadeeth, “The believers are bound by their conditions.” Al-‘Allaamah Ibn al-Qayyim said: It is obligatory to fulfil these conditions which are the most deserving of being fulfilled. This is what is implied by sharee’ah, reason and sound analogy, if the woman did not agree to become a man's wife except on these conditions, and if it were not obligatory to fulfil them, then the marriage contract would not be based on mutual agreement, and it would be making something obligatory upon her that Allah and His Messenger have not made obligatory. End quote. 

Al-Mulakhkhas al-Fiqhi (2/345, 346)