that she intended to buy Barira (a slave girl) and her masters stipulated that they would have her Wala'. When ʿAisha mentioned that to the Prophet ﷺ ; he said, "Buy her, for the Wala' is for the one who manumits."  

أَنْ تَشْتَرِيَ بَرِيرَةَ فَاشْتَرَطُوا عَلَيْهَا الْوَلاَءَ فَذَكَرَتْ ذَلِكَ لِلنَّبِيِّ ﷺ فَقَالَ اشْتَرِيهَا إِنَّمَا الْوَلاَءُ لِمَنْ أَعْتَقَ