What is the legal ruling if the landowner refused to return the amount paid as a down payment, did not specify a duration for that, and asked the buyer to be patient until after the war ends, knowing that the sale is not concluded until after the full payment of installments, and in case of failure to pay, the amount paid is to be returned after selling the plot of land?

If the duration of the remaining three installments for the land's price was not specified, then the sale is void due to the lack of a known term. In this case, the seller must immediately return the amount of the price received to the buyer, and it is not permissible for him to withhold it.

If the term of the installments was known, and it was stipulated that the sale would be annulled if the buyer was unable to pay the price, then the contract is a matter of dispute among scholars. If its invalidity is asserted, then its ruling is as stated above. If its validity is asserted, and then the buyer becomes unable, the sale is annulled, and the accelerated price must be returned immediately.

As for conditioning the return of the price on the sale of the land, this is void because it contradicts the implication of annulment, makes the term unknown, and involves uncertainty (gharar (definition)) and harm. Every condition that contravenes Allah's حكم (ruling) is void.