What is the ruling on a financial reward received from a usurious bank after training there, and is it permissible to give it out as an ongoing charity (Sadaqah Jariyah) if it is unlawful?

It is not permissible to work in a usurious bank, even for the purpose of training. What is earned from it is considered ill-gotten gain.

If a person is aware of the prohibition of such work, he must dispose of what he has earned by giving it to the poor and needy. He is not permitted to benefit from it himself unless he is poor and in need.

However, if he was ignorant of the prohibition of that work and only learned about it after the training period ended, then there is no blame upon him for benefiting from what he earned from it, due to the excuse of ignorance.