Sahih al-Bukhari, Hadith 2562 ⓘ
Narrated `Abdullah bin `Umar: Aisha wanted to buy a slave-girl in order to manumit her. The girl's masters stipulated that her Wala' would be for them. Allah's Messenger said (to `Aisha), "What they stipulate should not stop you, for the Wala' is for the liberator."
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ يُوسُفَ، أَخْبَرَنَا مَالِكٌ، عَنْ نَافِعٍ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ ـ رضى الله عنهما ـ قَالَ أَرَادَتْ عَائِشَةُ أُمُّ الْمُؤْمِنِينَ أَنْ تَشْتَرِيَ جَارِيَةً لِتُعْتِقَهَا، فَقَالَ أَهْلُهَا عَلَى أَنَّ وَلاَءَهَا لَنَا. قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " لاَ يَمْنَعُكِ ذَلِكِ، فَإِنَّمَا الْوَلاَءُ لِمَنْ أَعْتَقَ " .
also referenced under: Book 50, Hadith 3 (In-Book) & Volume 3, Book 46, Hadith 736 (USC-MSA)