Is zakat obligatory on money saved every four months when a year has passed, and is it to be paid multiple times a year or once, and is zakat obligatory on money from which zakat has already been paid?

Zakat is obligatory on saved wealth if it reaches the nisab (85 grams of gold or 595 grams of silver) and one hawl (lunar year) has passed on it. The hawl begins from the day of saving. If the saved amount is less than the nisab, it is combined with subsequent savings to complete the nisab, and the hawl is calculated from the date the nisab is reached. It is permissible to pay the zakat for multiple savings simultaneously when the hawl of the first one is due. Zakat is not obligatory on wealth for which zakat has already been paid, unless a new hawl passes on it and it reaches the nisab.