What is the ruling of the Sharia regarding a well-off person who does not spend on himself or his family; does his piety justify his stinginess?

Financial support (nafaqah) is obligatory upon a person for his ascendants, descendants, and wives, and he is not permitted to withhold it if he has the means. It is sufficient to give the obligatory amount, but it is better to be generous with them and with oneself, provided there is no extravagance.