What is the ruling on one who gathers onions and stores them until their price rises, in order to sell them?

It is permissible for a merchant to buy onions when they are cheap and abundant and to store them until their price increases. This is not a prohibited monopoly, as long as he did not buy them at a time of high prices and people's need. The prohibited monopoly is the hoarding of goods bought when prices are high, not when they are cheap, in order to sell them for more when the need becomes severe.