The sale of a monetary amount (thaman or naqd) in exchange for another monetary amount (thaman or naqd). More specifically, it is the exchange of one currency for another. In the pre-Islamic era, this type of sale was used to refer to the exchange of gold for gold, silver for silver, gold for silver or silver for gold. Under Islamic shari’ah, it used to mean the sale of price for price, where each price is regarded as consideration or countervalue for the other.

Ba’i al-thaman bil thaman (بيع الثمن بالثمن), also al-sarf or sarf, is an Arabic term that means “currency exchange“.