If somebody manumits a slave for expiation, for whom will the slave’s Wala be?

Narrated 'Aisha:

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

حَدَّثَنَا سُلَيْمَانُ بْنُ حَرْبٍ، حَدَّثَنَا شُعْبَةُ، عَنِ الْحَكَمِ، عَنْ إِبْرَاهِيمَ، عَنِ الأَسْوَدِ، عَنْ عَائِشَةَ، أَنَّهَا أَرَادَتْ أَنْ تَشْتَرِيَ، بَرِيرَةَ فَاشْتَرَطُوا عَلَيْهَا الْوَلاَءَ، فَذَكَرَتْ ذَلِكَ لِلنَّبِيِّ ﷺ فَقَالَ " اشْتَرِيهَا إِنَّمَا الْوَلاَءُ لِمَنْ أَعْتَقَ ".