What is the Sharia ruling regarding future commercial transactions in light of currency exchange rate fluctuations, and is it permissible to contract for a deferred sale without specifying the price at the time of the contract, on the condition that it be determined at the time of possession after 45 days, and are there any opinions from the madhhabs or scholars that permit this?

For a sale to be valid, the price must be known to both contracting parties at the time of the contract. Ignorance of the price invalidates the contract by consensus. The price must be money owned by the buyer, deliverable, and known in quantity and description. A sale is not valid if the price is the value of the sold item at a specific future date, as the price would then be unknown. Regarding the change in the purchasing power of currency, the general principle is that currencies are returned in their exact equivalents, regardless of changes in their power, unless the currency is no longer available in the market, in which case it is returned at its value on the day it became unavailable.