Narrated ‘A'isha said Barira came telling her she had arranged to buy her freedom for nine uqiyas; one to be paid annually, and asking her to help her. ‘A’isha replied, “If your people are willing that I should count them out to them all at one time and set you free, I shall do so, and I shall have the right:
What is the matter with people who make conditions which are not in God’s Book? Any condition which is not in God’s Book is worthless. Even if there are a hundred conditions, God’s decision is more valid and God's condition is more binding. The right of inheritance belongs only to the one who has set a person free.”
I was travelling on a camel of mine which had grown jaded when the Prophet passed by and struck it, with the result that it went as it had never done before. He then said, “Sell it to me for a wuqiya*”. I agreed, but made the stipulation that I should be allowed to ride it home. Then when I came to Medina I took the camel to him and he paid me its price in ready money. In a version he said, “He gave me its price and returned it to me." In a version by Bukhari he said to Bilal, “Pay him and give something extra," so he gave the money adding a qirat (A small coin, probably meaning here a sixteenth of a dirham).
(Bukhari and Muslim.)
*This and the more common form uqiya used below in the tradition from 'A'isha is an amount equivalent to forty dirhams.
Ibn ‘Umar reported God’s Messenger as saying, “If anyone buys palm-trees after they have been fecundated the fruit belongs to the seller unless the buyer makes a proviso; and if anyone buys a slave who possesses property his property belongs to the seller unless the buyer makes a proviso."
Muslim transmitted it and Bukhari transmitted something to the same effect as the first part alone.
