What is the legal consequence when a vow to fast coincides with the obligatory fasting of Ramadan?
General Chapter
Al-Mughni
Book of Vows
Primary text
When a person vows to fast, and that designated time falls within Ramadan, the single fast fulfills both the obligation of Ramadan and the vow. This is the view supported by the apparent statement of Al-Khiraqi and is the opinion of Abu Yusuf. This aligns with the reasoning of Ibn Abbas and 'Ikrimah, as one has fulfilled a vow of fasting during the very time one was already obligated to fast. Furthermore, if one vows a specific Hajj while an obligatory Hajj is due, performing the Hajj fulfills both obligations, according to a narration from Abu al-Khattab concerning Ahmad's view, mirroring Al-Khiraqi's statement. Similarly, 'Ikrimah, conveying Ibn Abbas, stated that if a man vows to perform Hajj but has not performed the obligatory Hajj, the single Hajj suffices for both the obligatory and the vowed Hajj.
Supporting text
The view held by Al-Qadi is that the vow itself does not take effect because it coincides with a time already prescribed for a required fast, similar to how a vow to fast on a day of obligatory fast would be void. However, the preferred opinion holds that the vow is valid because it is a vow of obedience that can usually be fulfilled, thus it takes effect, just as if it coincided with Sha'ban. Under this latter view, the person fasts Ramadan, then makes up the vow later, and also incurs the expiation (Kaffarah) for neglecting the vowed fast. Furthermore, Ibn Umar, Anas, and 'Urwah stated that the obligatory Hajj must be performed first, followed by the vowed Hajj.