Sahih al-Bukhari 2169
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."
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 ‏"‏‏.‏