What is the ruling on dealing with banks and the interest on money deposited therein, and what is the ruling on depositing large sums of money in Western banks and the returns therefrom, and what is the solution if there is a suspicion of unlawfulness in these interests, taking into consideration that leaving them to the banks may lead to their use against the Islamic religion?

The benefits from deposits in usurious banks are absolutely forbidden (haram (definition)) and the depositor is not permitted to own them, no matter their value. Rather, it is obligatory to dispose of them by spending them on charitable causes and for the benefit of Muslims. Leaving them with usurious banks is a mistake and strengthens usury. Their owners take them not for ownership, but to spend them on charitable causes.