ولا يجوز بيع الجيد بالرديء مما فيه الربا إلا مثلا بمثل
Translation: A superior-grade ribawi item may not be exchanged for an inferior-grade item of its genus except in an equal amount.
Superior quality does not authorize an unequal direct exchange within a ribawi genus. High-grade dates cannot be treated as if their better quality licenses a larger quantity of lower-grade dates on the other side.
For example, swapping 2 saʿ of premium dates directly for 3 saʿ of inferior dates violates the rule. Independent genuine sale transactions are different from disguising an unequal barter of the same genus.