Sahih Bukhari Volume 3, Book 34, Hadith Number 365.

Narated By Abdullah bin Umar : ‘Aisha wanted to buy Buraira and he (the Prophet) went out for the prayer. When he returned, she told him that they (her masters) refused to sell her except on the condition that her Wala’ would go to them. The Prophet replied, ‘The Wala’ would go to him who manumits.’ ” Hammam asked Nafi’ whether her (Buraira’s) husband was a free man or a slave. He replied that he did not know.