Is it permissible to give one's parents a refrigerator bought with ill-gotten money, or must it be kept without being used?

You are not obligated to dispose of what you bought with your salary from working in the Riba-based bank, and it is not forbidden to use it. You may benefit from the refrigerator or give it to your father. If you were aware of the unlawfulness of the work, you must dispose of the unlawful money. But if you were ignorant, then repentance suffices you by ceasing the work, regretting it, and seeking forgiveness. You are not required to dispose of what you earned, as Allah Almighty says: "Allah has forgiven what is past."