Is it permissible to sell iron safes to usurious banks?

The basic principle concerning selling is permissibility, unless it is coupled with aiding in an evil deed, in which case the sale becomes forbidden and the contract invalid. Examples include selling juice to someone who will turn it into wine, selling weapons during times of strife, selling a cup to someone who will drink wine in it, selling food to someone who will consume intoxicants with it, or selling weapons to highway robbers. This is based on Allah's saying: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." Accordingly, it is not permissible to sell safes to usurious banks, because doing so aids in the preservation of money that is forbidden by Islamic law.