What is the ruling if the arrival day is valid for fasting but the vow-maker is not fasting (neither obligatory nor voluntary) when the person arrives?

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There are two narrations concerning the person who vows to fast on a specific day, but when that day arrives, the vow-maker is breaking their fast (not fasting). One view states that qada' and kaffara are obligatory because a valid fast was vowed but not fulfilled, like other vowed obligations. Another view, held by Abu Yusuf and the People of Reason, is that nothing is due, as the arrival occurred on a day when fasting was not valid (i.e., the vow could not be fulfilled), similar to if the person arrived at night.