Arabic (ربا السنة) for riba associated with trading of goods that belong to the same genus and kind in different quantities. This riba which is mentioned in sunnah (traditions of the Prophet, peace be upon him) arises as a result of an excess in one of the countervalues over the other in a transaction involving two similar ribawi items (commodities susceptible to riba). Prohibition of riba al-sunnah is mainly based on prevention of law circumvention- i.e., sadd al-zhara’i or saddan lil-zhara’i) especially that spot trading of the same item for different quantities can be embedded in credit sales, paving the way for riba al-nasi’ah (riba associated with deferment or time factor). Furthermore, riba al-sunnah is prohibited because of the excessive degree of gharar (uncertainly) it usually involves (neither party is aware of the actual outcome of a given transaction- i.e., whether it would be to one’s benefit or harm).

Riba al-sunnah is also known as riba al-fadhl (riba al-fadl)- i.e., riba of excess (in quantity).