What is the Sharia ruling on a husband keeping money he saved from his divorced wife's salary, with her knowledge, and is this money considered his right in return for his effort in saving it?

If the money belongs to the wife and she did not permit her husband to take it, then the husband must return it to her, even if he was the one who saved it. However, if the wife is so imprudent as to warrant interdiction, then the money should not be given directly to her. Instead, it should be given to the Shariah judge or his representative, so that he may rule on the interdiction and appoint a guardian for the money.