أَخْبَرَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، قَالَ حَدَّثَنَا جَرِيرٌ، عَنْ مَنْصُورٍ، عَنْ إِبْرَاهِيمَ، عَنِ الأَسْوَدِ، عَنْ عَائِشَةَ، قَالَتِ اشْتَرَيْتُ بَرِيرَةَ فَاشْتَرَطَ أَهْلُهَا وَلاَءَهَا فَذَكَرْتُ ذَلِكَ لِلنَّبِيِّ صلى الله عليه وسلم فَقَالَ ‏"‏ أَعْتِقِيهَا فَإِنَّ الْوَلاَءَ لِمَنْ أَعْطَى الْوَرِقَ ‏"‏ ‏.‏ قَالَتْ فَأَعْتَقْتُهَا - قَالَتْ - فَدَعَاهَا رَسُولُ اللَّهِ صلى الله عليه وسلم فَخَيَّرَهَا مِنْ زَوْجِهَا فَاخْتَارَتْ نَفْسَهَا وَكَانَ زَوْجُهَا حُرًّا ‏.‏

It was narrated that 'Aishah said: "I bought Barirah and her masters stipulated that her loyalty (Wala) should be to them, I mentioned that to the Prophet and he said: 'Set her free, and loyalty belongs to the one who pays the silver.''' She said: "so I set her free. The Messenger of Allah called her and gave her the choice regarding her husband, and she chose herself. Her husband was a free man." Translation Not Available

Book Ref: Sunan An Nisai Book 44 Hadith 4642
Web Ref:  Sunan An Nisai Vol 5 Book 44 Hadith 4646