What is the ruling on parents' disapproval of lending money, even with knowledge of its virtue?

You are permitted to lend without their knowledge, because they do not have the right to prevent you from this lawful matter. However, demonstrate your obedience to them to avoid conflict. The Messenger of Allah, peace and blessings be upon him, said: "Obedience is only in what is good and right." And their prevention is not from what is good and right. If they fear the loss of the money, then lend with a pledge or guarantee to combine both interests. If they do not allow it, then lend secretly.