Is the questioner obligated to pay the amounts of checks he issued to his friends as guarantee checks, and is he sinful if he is compelled to take out an interest-bearing loan to pay them, especially since the original business owner is imprisoned and it is unknown when he will be released?

The entitlement of friends to the value of guarantee checks depends on their entitlement to a guarantee of the investment amount, and this occurs if the loss resulted from the negligence or transgression of the fund manager. If the questioner guaranteed the fund manager to his friends, he must pay the amount when it is proven. However, if the checks were merely to confirm participation, then he is not obligated to guarantee. If the questioner committed to guaranteeing the loss absolutely, then he must fulfill his promise. As for borrowing with interest (riba), it is forbidden by Islamic law and is not permissible except in cases of extreme necessity, such as imprisonment if the debtor cannot find anyone to lend him a benevolent loan. In such a case, he is permitted to the extent of the necessity. We advise searching for a benevolent loan first. If he cannot find one and is certain of imprisonment, then it is hoped that he will be permitted only to the extent of his debt.