Conditions not lawful in the marriage contract
حَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ مُوسَى، عَنْ زَكَرِيَّاءَ ـ هُوَ ابْنُ أَبِي زَائِدَةَ ـ عَنْ سَعْدِ بْنِ إِبْرَاهِيمَ، عَنْ أَبِي سَلَمَةَ، عَنْ أَبِي هُرَيْرَةَ ـ رضى الله عنه ـ عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " لاَ يَحِلُّ لاِمْرَأَةٍ تَسْأَلُ طَلاَقَ أُخْتِهَا لِتَسْتَفْرِغَ صَحْفَتَهَا، فَإِنَّمَا لَهَا مَا قُدِّرَ لَهَا ".
Narrated Abu Huraira: The Prophet (ﷺ) said, "It is not lawful for a woman (at the time of wedding) to ask for the divorce of her sister (i.e. the other wife of her would-be husband) in order to have everything for herself, for she will take only what has been written for her."