The World Federation One Stop Fiqh

Ruling 1529

It is not necessary for one to make an intention in his heart to fast, or to say, for example, ‘I will fast tomorrow’; rather, it is sufficient for one to decide that in humility to the Lord of the worlds, from the start of the time of ṣubḥ prayers until the time of maghrib prayers, he will not do anything that invalidates a fast. In order to be certain (i.e. have yaqīn) that one has fasted throughout this time, he must begin abstaining from a short period before the time of ṣubḥ prayers, and he must also refrain from doing anything that invalidates the fast for a short period after maghrib.