What is the ruling on selling a single commodity at different prices according to the change in the dollar exchange rate, knowing that its purchase price is fixed?

There is no specific limit to profit in Islamic law. Therefore, a merchant may profit 50%, 100%, or even more, provided that they do not sell the commodity for more than its market price, do not monopolize the commodity, do not deceive the buyer, and do not exploit the buyer's ignorance of prices. It is preferable for the merchant to act with gentleness, leniency, and contentment.

If a commodity is available everywhere and no one monopolizes it, there is no harm for the seller to take whatever profit they desire, unless they are profiting from an ignorant, naive person who does not know the prices. In this case, it is forbidden for them to profit more than what people usually profit from this commodity.

If you bought sugar for 3 pounds, then its price rose until it was sold for 15 pounds, and you did not monopolize it, there is no harm in selling it at this price. However, if you took into account that you bought it cheaply and sold it for 10 or 12 pounds, it would be better for you, due to the kindness and benevolence it entails for people.

It is not permissible for you to sell a commodity at a price you expect it to rise to, nor to refrain from selling it when it is available to you and people need it, waiting for its price to rise. This is a forbidden form of monopolization.