Is it permissible for the wife to secretly take money from her husband to buy the children's necessities and save part of it, knowing that her husband is wealthy but stingy in spending?

It is unlawful for a wife to take her husband's money without his knowledge, unless he is stingy with her and their children regarding maintenance. In that case, she may take what is sufficient for her and her child, in a reasonable manner, without excess, even if her intention is to save it.