Sahih Bukhari Volume 8, Book 80, Hadith Number 749.

Narrated By Ibn Umar : That ‘Aisha, the mother of the Believers, intended to buy a slave girl in order to manumit her. The slave girl’s master said, “We are ready to sell her to you on the condition that her Wala should be for us.” ‘Aisha mentioned that to Allah’s Apostle who said, “This (condition) should not prevent you from buying her, for the Wala is for the one who manumits (the slave).”