What is the ruling on buying or selling something at a predetermined future price, such that profit and loss depend on the price of that item at the agreed-upon time of sale or purchase?

It is permissible to purchase a described good for a known future delivery, by paying the full price at the time of the contract. This is known as a forward contract (Salam), based on the Prophet Muhammad’s (peace be upon him) saying: "Whoever pays in advance for something; let it be for a known measure, a known weight, and to a known term." The seller is obligated to deliver the good at the specified time. Profit or loss is realized by both the buyer and the seller based on the price of the good at the time of delivery compared to its purchase price. This contract is permissible by the Qur’an, Sunnah, and scholarly consensus due to people's need for it, and the buyer often benefits from a lower price. It must be noted that the sale occurs upon the payment of the price, and what is deferred is the delivery of the good, not the contract itself being deferred or suspended.