What is the legal ruling on reserving gold ingots by agreeing upon a specific price, then receiving them and paying the price a day or two later, with the agreement not being affected by fluctuations in the price of gold?

It is a condition for the sale of gold for gold, silver, or money that both عوضان (countervalues) be present at the عقد (contract) assembly, and that the exchange be hand-to-hand (immediate قبض - acquisition), otherwise, it would be considered Riba Al-Nasi'ah (interest due to delay). Paper currency takes the same ruling as silver in this condition; therefore, it is not permissible to sell gold for money unless it is hand-to-hand. It is permissible to make inquiries to ascertain the price and quantity, but the purchase is not concluded until the gold is exchanged for money at the contract assembly, and the decisive price is that at the time of contracting.