If somebody imposes conditions in selling against the Islamic Law
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ يُوسُفَ، أَخْبَرَنَا مَالِكٌ، عَنْ نَافِعٍ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ ـ رضى الله عنهما ـ أَنَّ عَائِشَةَ، أُمَّ الْمُؤْمِنِينَ أَرَادَتْ أَنْ تَشْتَرِيَ جَارِيَةً فَتُعْتِقَهَا، فَقَالَ أَهْلُهَا نَبِيعُكِهَا عَلَى أَنَّ وَلاَءَهَا لَنَا. فَذَكَرَتْ ذَلِكَ لِرَسُولِ اللَّهِ صلى الله عليه وسلم فَقَالَ " لاَ يَمْنَعُكِ ذَلِكَ، فَإِنَّمَا الْوَلاَءُ لِمَنْ أَعْتَقَ ".
Narrated `Abdullah bin `Umar: Aisha, (mother of the faithful believers) wanted to buy a slave girl and manumit her, but her masters said that they would sell her only on the condition that her Wala' would be for them. `Aisha told Allah's Messenger (ﷺ) of that. He said, "What they stipulate should not hinder you from buying her, as the Wala' is for the manumitted."