Is the money saved in the post office without interest forbidden or permissible, and is it the cause of the son's illness?

Depositing money in usurious institutions, including current accounts, is not permissible because it assists them in usury, and these are institutions that wage war against Allah and His Messenger. The money must be withdrawn from the Post Office and one must repent to Allah. As for the son's illness, sins are a cause for calamities to befall, as Ibn al-Qayyim said: "No blessing has ever been removed from a servant except due to a sin, and no adversity has ever befallen him except due to a sin." He cited the saying of Ali ibn Abi Talib, may Allah be pleased with him: "No affliction descends except due to a sin, and no affliction is removed except through repentance," and Allah’s saying: "And whatever strikes you of disaster - it is for what your hands have earned, and He pardons much." And Allah’s saying: "That is because Allah would not change a favor which He had bestowed upon a people until they change what is within themselves," and "Indeed, Allah will not change the condition of a people until they change what is in themselves." If one changes disobedience to obedience, Allah will change punishment to well-being.