The World Federation One Stop Fiqh

Ruling 2306

If a person gives something to someone so that he may take a greater amount in another city, and if the item is gold, silver, wheat, or barley which can be weighed or measured, it is usury and unlawful. However, if the party that is taking the extra amount gives or does something in return, there is no problem. If bank notes are given on loan, it is not permitted to take back more. If a person sells them as an immediate exchange (naqd)1 transaction, or on credit (nasīʾah) but the money is in two currencies, such as pounds sterling and dollars, then there is no problem with any extra received. However, if it is a credit sale and the money is in one currency only, then receiving an extra amount is problematic (maḥall al‑ishkāl) [i.e. based on obligatory precaution, it is to be avoided].2
1 In an immediate exchange transaction, there is no lapse of time between the buyer paying for the item and receiving it.
2 As mentioned in Ruling 6, the term ‘problematic’ (maḥall al‑ishkāl) amounts to saying that the ruling is based on obligatory precaution.