A sale (ba’i) contract that involves the exchange of a monetary item (gold, silver, currency) for another monetary item, or in general, athman. In other words, it is an exchange of thaman (currency unit/ a form of money) for another at a specific rate. Under shari’ah, this type of sale is subject to a set of strict rules as to the sarf or exchange transaction, including, for example, simultaneous taqabudh (qabdh and taqbeedh at the same contracting session- majlis al-aqd), and in case of an exchange of two countervalues belonging to the same genus (like, gold for gold), the exchanged amounts must be equal. Otherwise, ba’i al-athman may give rise to riba in many forms (like riba al-fadhl, riba al-nasi’ah, and riba al-nasa’a).

Ba’i al-athman is also known as ba’i al-sarf.