Sunan an-Nasa'i 4642
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."
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 ‏.‏