[A Man Placed His Money in the Bank, and When He Withdrew It He Gave the Increase in Charity]

Answer: A man may be excused in such a case if he put his money in the bank for the first time, not knowing that the bank pays interest. But if he knows that the bank pays interest to anyone who deposits money with it, then it is not permissible for him to deposit his money there, because:
The bank is, in reality, established to trade with everything deposited with it, in return for a monetary percentage paid to the depositor each month. What is deposited in the bank is not, in truth, a “deposit” (wadīʿah); rather, it is a loan the bank takes to benefit from, for which it pays the lender “interest.” Thus, depositing in the bank is in fact a loan that draws a benefit.
If it is said: The depositor’s intention may be merely safeguarding his wealth—he has no intention of receiving interest; another may intend and seek interest and profit. “Actions are by intentions.” Hence, there would be no blame on one who has no intention to seek profit and whose aim is only the safekeeping of his money—unlike the one who intends and seeks profit.
It is said: A transaction whose nature and established function is to produce the forbidden benefit is prohibited absolutely—whether one intends that benefit or not. Committing a sin does not require an intention.
Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2