Is money saved from lying to a stingy father considered unlawful wealth?

If a son has his own money, the father is not obligated to spend on him. You erred by lying to your father that you had no money, compelling him to spend on you. You must repent to Allah and compensate him for what he spent due to your lie, unless he forgives you. The compensation does not necessarily have to be direct. Your description of your father as stingy is impermissible, as he did not withhold any right that was obligatory upon him, and he bought you a car for a large sum. If the money you possess to compensate your father is the same money you acquired by lying to him, then it is not permissible for you to invest it, because his right is attached to it. We advise you to inform your father of the truth of the matter; most likely, he will forgive you and bless your project.