Is the intention to fast valid if the person doubts whether the next day is Ramadan, without a firm basis for that assumption (e.g., on the thirtieth night of Sha'ban without a clear horizon)?
General Chapter
Al-Mughni
Book of Fasting
Primary text
The intention is invalid and the fast is not accepted if one intends to fast the next day, suspecting it might be Ramadan, but lacking any basis or certainty for this assumption, such as on the thirtieth night of Sha'ban when there is no obstruction to sighting the moon. This is because the intention must follow knowledge, and a purpose based on something unknown, without evidence or firm belief, is invalid. This position is held by Hammad, Rabi'ah, Malik, Ibn Abi Layla, Al-Hasan bin Salih, and Ibn al-Mundhir. The evidence against validity is that the intention was not definitively made for a fast from Ramadan, mirroring the invalidity if knowledge comes after the time for intention has passed.
Supporting text
Al-Thawri and Al-Awza'i hold that the intention is valid if made from the night because the intention to fast from the night itself is sound, similar to the second day of fasting. A narration from Al-Shafi'i reflects both opinions. Furthermore, building an intention based on the say-so of astrologers or calculators, even if often correct, is invalid as it is not a legislated proof, mirroring the ruling of the Prophet, peace be upon him: 'Fast upon seeing it, and break the fast upon seeing it,' and in another narration, 'Do not fast until you see it, nor break the fast until you see it.'