Ruling 1531 — Fasting (Ṣawm)

The latest time available for a conscious person to make the intention to keep a fast of the month of Ramadan is at the time of ṣubḥ prayers. This means that, based on obligatory precaution (al‑iḥtiyāṭ al‑wājib), at the time of ṣubḥ his abstinence [from the eight things that invalidate a fast] must coincide with his intention to fast, albeit subconsciously.