ويجوز للبائع أن يزيد في المبيع
Translation: The seller may increase what is transferred as the sale object.
A seller may, under the relevant conditions and agreement, add an identified item to what was sold—for instance, the original ten bags are supplemented by one specified additional bag.
Adding to the goods and adding to the price are distinct: one changes the transferred asset, the other changes the buyer’s consideration. The commentaries discuss how such adjustments relate to the original transaction.