If a person vows to give charity using specific existing money (e.g., 200 dirhams) upon the passing of the Hawl (one lunar year), does Zakat apply to that specific amount?
Chapter on Zakat on Debt and Charity
Al-Mughni
Book of Zakat
Primary text
Ibn 'Aqil stated that the amount vowed is given to fulfill the vow, and Zakat is not obligatory upon him for that amount because the vow is considered more emphasized as it is tied to the specific asset, whereas the obligation of Zakat is disputed. Consequently, the vow takes precedence, and the specific asset is used for it.
Supporting text
Alternatively, it is possible that Zakat is also obligatory upon him for that amount, and the charity given fulfills both the vow and the Zakat, provided he intends the Zakat amount specifically within the payment. Since Zakat is a form of charity, the rest fulfills the vow.