Is it considered forbidden or a monopoly to keep a quantity of a certain crop for the purpose of trading it when its price rises to make a profit?

Purchasing an item when its price is low and holding onto it until its price rises, then selling it, is not considered a forbidden monopoly. The forbidden monopoly is the withholding of food, sustenance, and all necessities that people need during times of high prices, in order to make them even more expensive for them.