Now change one detail in the fixed-day-vow example: before true dawn, the person intended another obligatory fast.
Then that other obligatory fast is performed, and the fixed-day vowed fast remains to be made up as Qada.
This differs from making that other intention only after dawn, before Nisf al-Nahar, with no pre-dawn intention: that case counted as the fixed-day vowed fast.
It also differs from Ramadan. In the Ramadan example, even intending another obligatory fast before dawn still counts as the Ramadan fast. A named vow-day and Ramadan's prescribed time do not have identical effects.
- What Changes if the Other Intention Was Before Dawn?