Is zakat obligatory on the debt owed by the husband to his wife?

The debts owed by a husband to his wife have two situations regarding zakat: If the husband is financially well-off and not a procrastinator, and the wife can collect the debt upon demanding it, then zakat is due on it every year. However, if the husband is not in such a condition, then there is no zakat on the debt. Nevertheless, it is recommended to pay zakat on it for one year when it is collected, even if the debt remained for years. As for the deferred dowry (mu'akhkhar) that the wife does not receive except after separation, there is no zakat on it until she collects it, and it is recommended to pay zakat on it for one year upon collection.

If the wife's money alone does not reach the nisab (minimum threshold), then there is no zakat on it, as she has an independent financial ذمة (legal personality/liability). If it reaches the nisab, zakat becomes obligatory on it.

In summary: It is permissible to combine the husband's money, the wife's money, and her debts owed by him to pay zakat on all of them, unless the husband is in financial hardship, in which case there is no zakat on the debt. Similarly, there is no zakat on the deferred dowry if the husband is poor, or if the custom is that the wife does not become entitled to it except after separation.