What is the ruling of Islam on purchasing agricultural crops before their season, and is it necessary to specify their price? And what is the ruling on purchasing them after they have been harvested without specifying their price, then settling the payment based on the first price at which the crop appears?

It is not permissible to sell agricultural crops before their suitability for harvesting becomes apparent, due to the element of gharar (uncertainty/risk) and the prohibition thereof. However, once their suitability becomes apparent, it is permissible to sell them. The seller is responsible for irrigation. If the crop is afflicted by a pest or disease before harvesting, the price is forfeited. It is not permissible to sell fruit for several years in advance. It is permissible to enter into a salam contract by paying a known price in advance for a known weight or measure of produce or fruit to be delivered after a known period, provided that the commodity is available at the time of delivery. It is not permissible to sell without knowing the price, because this invalidates the contract due to the lack of knowledge concerning the price and the item being sold.