Is the explicit intention (ta'yeen) required for every obligatory fast?
General Chapter
Al-Mughni
Book of Fasting
Primary text
The explicit intention stating which obligatory fast one is undertaking is required for every obligatory fast. This means believing that one is fasting tomorrow from Ramadan, its make-up (qada'), its expiation (kaffarah), or a vow. Ahmad, according to the narration of Al-Athram, affirmed this, stating that a person fasting during Ramadan in enemy territory without knowing it was Ramadan would not have their fast suffice unless they had the firm intention that it was from Ramadan. Similarly, the fast on the Day of Doubt is not valid if one awakens intending to fast unless there is a firm intention from the night that it is Ramadan. Malik and Al-Shafi'i hold this view.
Supporting text
There is another narration from Ahmad stating that specifying the intention for Ramadan is not obligatory. Al-Marwadhi narrated that Ahmad agreed that on the Day of Doubt, if one decides from the night to wake up fasting, it suffices for Ramadan, even without the specific belief that it is Ramadan, citing the general principle that "actions are but by intentions" as not necessarily requiring the specific identification of Ramadan.