Which obligation takes precedence: making up a missed Ramadan fast or fulfilling a vow to fast?

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If making up a missed Ramadan fast or another required Kaffarah is necessary, it must be performed before fulfilling the vow to fast. This precedence is given because the Ramadan makeup fast is an obligation stemming from the fundamental divine law, thus taking priority over obligations undertaken by oneself, similar to prioritizing the obligatory Hajj over a vowed Hajj.