Surety | Islamic Laws by The Leader Ayatullah Ali Khamenei

Q1668. Is it permissible for a person, who has no funds in the bank, to write a check with a view to standing surety for someone else?
A: There is no objection to doing so. The validity of a surety deed and giving a check as a surety does not depend on having a positive bank balance at the time of standing surety and making out the check.
Q1669. I lent someone a sum of money, which he did not pay back. A relative of his wrote me a post-dated check for the amount of the debt provided that I allow him some time [to settle the debt]. Thus, he undertook to pay me back the debt if the original debtor defaulted. The debtor ran away without leaving a trace, so much so that I lost every contact with him. Is it shari that I get back the whole amount of debt from the surety?
A: If the person stood as surety in a shari way, should the debtor default, you are permitted, after the date of repayment has passed, to demand the repayment of the whole amount of the debt.