Sahih Bukhari
Laws of Inheritance (Al-Faraaid)
Volume: 008 / Book Number: 080 / Hadith Number: 751
Narrated Ibn Umar:
When Aisha intended to buy Barira, she said to the Prophet, "Barira's masters stipulated that they will have the Wala." The Prophet said (to Aisha), "Buy her, as the Wala is for the one who manumits."