Is a bank loan that is repaid with an increase over the original amount permissible or forbidden, and what should I do with the money if there is doubt about it?

Working in usurious banks and with interest-bearing loans is forbidden. Whoever works in them must repent and immediately cease. As for the money spent previously, before repentance, there is no sin in it, for Allah the Almighty says: "So whoever receives an admonition from his Lord and desists, he shall be entitled to keep what he earned in the past; his affair rests with Allah." As for what remains of these funds, it must be spent on general Muslim welfare, such as building hospitals and schools and assisting the needy. Similarly, a loan repaid with unlawful money must be spent on the same types of beneficiaries. However, if the usurious loan was repaid with lawful money, then there is no sin in benefiting from it, while repentance and seeking forgiveness remain obligatory.