Allah, Exalted is He, has deemed buying and selling lawful for His Muslim servants, but deemed Ribaa (i.e., interest, usury) unlawful. He Says (what means): {…they said, “Trade is [just] like Ribaa." But Allah has permitted trade and has forbidden Ribaa.} [Quran 2:275]. In this hadeeth, the Prophet ﷺ forbids forms of Ribaa involved in the sale of gold and silver, and teaches the lawful ways of buying and selling gold and silver, to avoid falling into what is unlawful. He ﷺ said: “Do not sell gold for gold unless equal in weight,” meaning that the two exchanged commodities must be equal in weight; twenty grams of gold may not be sold for thirty grams of gold for example, and such increase is labelled as Ribaa. The same goes for silver and paper money (i.e., currency exchange). Afterward, the Prophet ﷺ said: “… do not sell gold or silver that is not present at the moment of exchange for gold or silver that is present,” meaning do not sell gold or silver to be delivered at a deferred time for an immediate payment (of gold or silver) made at the contracting session. By analogy, the same ruling applies to all sale transactions in which the exchanged commodities share the same ‘Illah (i.e., underlying legal reason that necessitates the effective cause of the ruling which then leads to its enactment), which is being used as currency (i.e., Thamaniyyah) in case of the gold and silver. Likewise, the ruling applies to whatever is being used as currency, like paper money, and is subject to Ribaa in such sale transactions. There are two conditions stipulated for the validity of the sale (exchange) of similar commodities: being equal in weight, and immediate hand-to-hand exchange in the contracting session. If the exchanged commodities are dissimilar, e.g., gold for silver or the other way round, but the ‘Illah is the same, i.e., being used as currency, the requirement of being equal in weight is no longer stipulated, yet the immediate hand-to-hand exchange in the contracting session is required. The Prophet ﷺ said: “…if the exchanged commodities of a barter are dissimilar, sell as you wish as long as they are exchanged hand to hand (i.e., on the spot).” [Muslim]. .