Narrated `Aisha
Allah's Messenger (ﷺ) came to me and I told him about the slave-girl (Buraira) Allah's Messenger (ﷺ) said, "Buy and manumit her, for the Wala is for the one who manumits." In the evening the Prophet (ﷺ) got up and glorified Allah as He deserved and then said, "Why do some people impose conditions which are not present in Allah's Book (Laws)? Whoever imposes such a condition as is not in Allah's Laws, then that condition is invalid even if he imposes one hundred conditions, for Allah's conditions are more binding and reliable."
Narrated `Abdullah bin `Umar
Aisha wanted to buy Buraira and he (the Prophet (ﷺ) ) 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 (ﷺ) 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.