Q: What is your opinion - May Allah grant you success - about
depositing money in banks that deal with Riba (usury/interest),
and using the depositors' money in Riba- based transactions, knowing that these depositors can protect their money from theft by putting them in strong safes?
If the bank uses the depositors' money to conduct Riba-based transactions, at the same time when money owners can keep their money safe from theft and such things by means that do not involve Riba- it becomes impermissible for them to deposit their money in banks or any other entities that conduct prohibited transactions, by which they seek assistance in committing sins. This is because the means to evil is evil in itself, and helping to commit what is prohibited is Haram (prohibited), and this takes the same ruling of intentions. (Part No. 13; Page No. 344)
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.