From Sahih Bukhari (Hadith 6759):
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 (ﷺ) said (to Aisha), "Buy her, as the Wala is for the one who manumits
Reference: Bukhari 6759