What is the ruling on annulling an installment sale contract or extending its period after two installments have been paid, given the buyer's inability to pay the remaining installments?

Extending the installment period is permissible if it does not result in an increase in the price. However, if it results in an increase, then it is prohibited usury (riba). Allah Almighty says: "O you who have believed, fear Allah and give up what remains [due to you] of interest, if you should be believers. And if you do not, then be informed of a war [against you] from Allah and His Messenger." In the event that the debtor is unable to pay, the creditor must grant him a respite until a time of ease, as Allah Almighty says: "And if there is any with difficulty, then grant him time until a state of ease."