What is the ruling on keeping money in banks with interest on it, and is it obligatory to leave this interest, or to take it and donate it to the poor, or is it considered lawful money?

It is not permissible to deposit money in an interest-based (usurious) bank when there is ample choice and alternatives, whether it is a current account or a savings account. If a Muslim is compelled to do so, fearing for his money and finding no Islamic alternative, then he is permitted to place it in a current account only, not in a savings account, to avoid dealing with usury. Whoever deposits it in a savings account or without necessity, must repent and dispose of the usurious interest by spending it on charitable and good causes.