The World Federation One Stop Fiqh

Ruling 1531

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.