Is it permissible to take compensation for a defect (Arsh al-'Ayb) when exchanging currency (Sarf) of the same type?

Primary text

It is impermissible to take compensation for a defect when exchanging currency of the same genus. This is prohibited because it results in an increase in one of the exchanged items, violating the condition of equality (Muthilat) required in exchange of the same genus. The compensation for defect is considered part of the exchange value, as it is used to settle accounts in Murabaha transactions, is taken by the preemptor (Shufi'), and is returned upon rescission or mutual dissolution of the contract. If the Arsh were not considered part of the exchange value, the buyer would have no basis for acquiring it, as it is not a gift. The condition of equality pertains even to the immediate setting (Majlis) of the transaction.