the fact that, in the jurists’ view, thamaniyyah (the quality of functioning as a price) is not confined to gold and silver—although those two metals are its original form—and since paper currency has itself become the medium of exchange, taking the place of gold and silver in commercial dealings; and because, in our time, objects are valued in it after transactions in gold and silver have virtually disappeared, and payment and discharge of debts are effected with it, even though its worth does not lie in the paper itself but in something extrinsic to it; and whereas close examination shows that the operative cause for the prohibition of ribā in gold and silver is absolute thamaniyyah, a quality that is likewise present in paper money—therefore the Islamic Fiqh Council hereby rules: paper currency is an independent form of money subject to the same rulings that apply to the two precious metals. Zakāt is therefore obligatory on it, and both kinds of ribā—excess (faḍl) and deferment (nasāʾ)—run in it exactly as they run in gold and silver, by analogy based on its thamaniyyah. Consequently, paper money carries all the legal consequences of currency in every obligation imposed by the Sharīʿah, and no other consideration is of relevance. Thamaniyyah has thus become the decisive cause in every monetary medium, whatever its form may be.”

Resolution of the Islamic Fiqh Council concerning Gold Trading and the Sharīʿah Solutions for the Combination of Ṣarf and Ḥawālah: Resolution No. 84:

The Islamic Fiqh Council, convened in its ninth session in Abu Dhabi, United Arab Emirates, from 1–6 Dhū al-Qaʿdah 1415 AH (1–6 April 1995 CE),
after reviewing the papers submitted to the Council on the subject of “Gold Trading and the Sharīʿah Solutions for the Combination of Currency Exchange and Transfer,” and after listening to the discussions that took place,