Is zakat obligatory for a ready-made clothes merchant whose money accumulates from cash sales and debts, and is used to purchase new merchandise, while he has no saved money and most of his debts are not collected until after years?

The value of trade goods and capital owned by a merchant must be assessed at the end of each year (hawl), and outstanding debts owed to him by others should be added to them. If the total reaches the nisab, zakat becomes obligatory on it. It is permissible to delay paying zakat on outstanding debts until they are collected, and then zakat for the past years is paid.