From Sahih Bukhari (Hadith 2169):
Narrated `Abdullah bin `Umar:Aisha, (mother of the faithful believers) wanted to buy a slave girl and manumit her, but her masters said that they would sell her only on the condition that her Wala' would be for them. `Aisha told Allah's Messenger (ﷺ) of that. He said, "What they stipulate should not hinder you from buying her, as the Wala' is for the manumitted
Reference: Bukhari 2169