Is zakat obligatory on money saved from trade if a hawl passes over it, and on the salary from which nothing has been saved?

The lunar months are what count in calculating zakat, and the error in relying on the solar year is corrected by ascertaining the beginning of the first lunar year in which zakat became due. Zakat becomes obligatory on an amount if a hawl (lunar year) has passed over it while it constitutes a nisab (minimum taxable amount) by itself or by adding other money or trade goods to it. There is no zakat on an amount invested in trade before its hawl, unless it resulted from an existing nisab; in which case, the profit's hawl follows the principal's. However, if it did not result from it, its zakat becomes due when its hawl passes, even if it does not reach the nisab, because it is a تابع (dependent) on the existing nisab in the bank. It is permissible to pay zakat on all wealth at once when the hawl of the deposited money is due. Depositing money in interest-based banks is forbidden, and one must repent and withdraw the money. Interest-based earnings are not subject to zakat; rather, they must be disposed of by giving them as charity to the poor and needy or spending them on the welfare of Muslims.