What is the ruling on someone who intended to sell gold, then exchanged it for something else after forgetting the initial intention, and what is the expiation for this mistake?

The merchant's exchange of gold for gold with an increase is a void contract, because the exchange of gold for gold requires equality and immediate possession. Whoever gives or takes an increase has engaged in usury.

However, if the annulment of the contract is not possible, one may adopt the opinion that considers manufactured jewelry as a commodity not subject to monetary regulations, and thus, usury does not apply to it.

This view was supported by Ibn al-Qayyim and Ibn Taymiyyah, who held that the increase in manufactured gold is in exchange for the permissible craftsmanship, and that the prohibition of differential exchange does not apply between it and monetary prices, just as it does not apply between monetary prices and other commodities. This is also what necessity calls for.