We are prepared to sell her to you on the condition that her right of inheritance would vest with you. She (Hadrat A'isha) made a mention of that to Allah's Messenger (ﷺ) whereupon he said: This should not stand in your way. The right of inheritance vests in one who emancipates.
Sahih Muslim Book 20, Hadith 7
← Previous Hadith A hadith like this is reported on the authority of the same chain of transmitters but with a slight change of words.

Sahih Muslim Book 20, Hadith 6 Next Hadith → If she (Hadrat 'A'isha) wants to do good to You for the sake of Allah, she may do it, but the right of inheritance will be ours. She (Hadrat 'A'isha) made a mention of that to Allah's Messenger (ﷺ), and he said to her: Buy her, and emancipate her, for the right of inheritance vests with one who emancipates (the slave). Allah's Messenger, may peace be upon him) then stood up and said: What has happened to the people that they lay down conditions which are not (found) in the Book of Allah? And he who laid down a condition not found in the Book of Allah, that is not valid. even if it is laid down hundred times. The condition laid down by Allah is the most weighty and the most valid.

Sahih Muslim Book 20, Hadith 8