Is it permissible to deposit money in an Islamic bank with a monthly return, and then spend the questionable return (usury/interest) on charitable causes such as building hospitals and restrooms?

It is not permissible to deal with usurious banks for the purpose of taking interest and using it for the benefit of Muslims, as this involves striving to acquire unlawful money and aiding those banks in sin. As for one who repents from usurious transactions, the interest is not lawful for him, and he must dispose of it by spending it on thealthings that benefit Muslims, and not by leaving it with the banks. However, dealing with Islamic banks that adhere to Sharia (definition) is permissible, and their profits are lawful.