Sahih al-Bukhari 2564
Narrated `Amra bint `Abdur-Rahman:
Barirah went to Aisha, the mother of the faithful believers to seek her help in her emancipation Aisha 
said to her, "If your masters agree, I will pay them your price in a lump sum and manumit (free) you." 
Barirah mentioned that offer to her masters but they refused to sell her unless the Wala' was for them. 
`Aisha told Allah's Messenger (ﷺ) about it. He said, "Buy and manumit her as the Wala' is for the liberator."
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ يُوسُفَ، أَخْبَرَنَا مَالِكٌ، عَنْ يَحْيَى بْنِ سَعِيدٍ، عَنْ عَمْرَةَ بِنْتِ عَبْدِ الرَّحْمَنِ، أَنَّ بَرِيرَةَ، جَاءَتْ تَسْتَعِينُ عَائِشَةَ أُمَّ الْمُؤْمِنِينَ ـ رضى الله عنها ـ فَقَالَتْ لَهَا إِنْ أَحَبَّ أَهْلُكِ أَنْ أَصُبَّ لَهُمْ ثَمَنَكِ صَبَّةً وَاحِدَةً فَأُعْتِقَكِ فَعَلْتُ‏.‏ فَذَكَرَتْ بَرِيرَةُ ذَلِكَ لأَهْلِهَا، فَقَالُوا لاَ‏.‏ إِلاَّ أَنْ يَكُونَ وَلاَؤُكِ لَنَا‏.‏ قَالَ مَالِكٌ قَالَ يَحْيَى فَزَعَمَتْ عَمْرَةُ أَنَّ عَائِشَةَ ذَكَرَتْ ذَلِكَ لِرَسُولِ اللَّهِ صلى الله عليه وسلم فَقَالَ ‏
"‏ اشْتَرِيهَا وَأَعْتِقِيهَا، فَإِنَّمَا الْوَلاَءُ لِمَنْ أَعْتَقَ ‏"‏‏.‏