Muwatta 1835

Malik was asked about a man who buys an orchard from a man that has varieties of palms, such as ajwa, kabis and a cluster, and other kinds of dates, and makes an exception for the fruit of one or more palms he chooses from it. Malik said: that is not proper. If he does that, he leaves the fruit of an ajwa palm, which yields fifteen sa's, and takes in its place the fruit of a kabis palm, which yields ten sa's. If he takes the ajwa which yields fifteen sa's and leaves the kabis which yields ten sa's, it is as if he bought ajwa for kabis with unequal measures. ¹

Belongs to the Muwatta, Book of Sales. Source: the Muwatta. Mentions Malik ibn Anas. Built on in the chapters on exceptions in sale and riba.