Sahih al-Bukhari 2721
Sahih al-Bukhari · Book 54: Conditions · The terms and the conditions of Mahr
Narrated `Uqba bin Amir:
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ يُوسُفَ ، حَدَّثَنَا اللَّيْثُ ، قَالَ حَدَّثَنِي يَزِيدُ بْنُ أَبِي حَبِيبٍ ، عَنْ أَبِي الْخَيْرِ ، عَنْ عُقْبَةَ بْنِ عَامِرٍ ـ رضى الله عنه ـ قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " أَحَقُّ الشُّرُوطِ أَنْ تُوفُوا بِهِ مَا اسْتَحْلَلْتُمْ بِهِ الْفُرُوجَ " .
Allah's Messenger (ﷺ) said, "From among all the conditions which you have to fulfill, the conditions which make it legal for you to have sexual relations (i.e. the marriage contract) have the greatest right to be fulfilled."