Do not sell gold for gold, except like for like, and don't increase something of it upon something; and don't sell silver unless like for like, and don't increase some thing of it upon something, and do not sell for ready money something to be given later.
The Book of Musaqah
Author: Sahih Muslim | Hadith Reference: Sahih Muslim 1584 a
Hadith Text
Do not sell gold for gold, except like for like, and don't increase something of it upon something; and don't sell silver unless like for like, and don't increase some thing of it upon something, and do not sell for ready money something to be given later.
Commentary on Riba al-Fadl
This prohibition establishes the fundamental principle of Riba al-Fadl (excess interest) in exchange of homogeneous commodities. Gold and silver, being monetary standards, must be exchanged equal for equal in both quantity and immediate possession to prevent usury.
The condition "like for like" requires identical weight and purity when exchanging the same metal type. The prohibition against "increase" forbids any disparity in quantity, even if quality differs, as this creates hidden usury.
Commentary on Riba al-Nasi'ah
The final prohibition addresses Riba al-Nasi'ah (delay interest), forbidding deferred exchange in homogeneous commodities. When items are of the same genus and function as currency, both hand-to-hand delivery and equal measure are required simultaneously.
This ruling applies to the six commodities mentioned in prophetic traditions: gold, silver, wheat, barley, dates, and salt. Any exchange of these identical items requires immediate reciprocal possession to prevent temporal advantage constituting usury.
Legal Wisdom
These regulations preserve economic justice by eliminating exploitative exchanges where substance is identical but terms create unfair advantage. The wisdom lies in closing potential avenues for usury while maintaining legitimate trade channels.
Scholars derive from this that when medium of exchange commodities are traded for themselves, only spot transactions with exact equivalence are permitted, ensuring purity of transactions and prevention of economic oppression.