Consensus (ijmāʿ)
No disagreement has been transmitted to us from any of the great Imams on this point.
Those for whom the fast is unconditionally obligatory
The duty falls upon every person who is: (1) adult, (2) of sound mind, (3) resident, and (4) physically able—provided no factor preventing the fast is present. For women, the preventing factor is menstruation. There is no dispute about this, because the Exalted says,
“So whoever of you witnesses the month, let him fast it.” (Q 2:185)
The Second Discussion: The Pillars of Fasting
The First Pillar: The Time-Frame
The pillars are three. Two are unanimously accepted—(1) the time-frame and (2) abstention from the nullifiers—and a third is disputed, namely (3) the intention (niyyah).
The first pillar, time, is divided into two parts:
- The time when the obligation itself arises, that is, the month of Ramadan; and
- The time during which abstention from the nullifiers is required, namely the days of that month, excluding its nights.
Each of these two periods gives rise to foundational questions over which the jurists differed. Let us begin with those concerning the time of obligation.
First: determining the two limits of that time (its beginning and end);
Second: identifying the means by which each individual and locality can establish the definitive sign that marks those limits.
As to the two limits: the scholars unanimously agree that an Arabic lunar month may be twenty-nine days or thirty, and that the standard for determining the month of Ramadan is the crescent’s sighting, based on the Prophet’s—peace and blessings upon him—words: “Fast when you see it, and break your fast when you see it.” By “sighting” he meant the crescent’s first visible appearance after the sun has passed the meridian.
They disagreed, however, about the ruling when the sky is overcast and sighting is impossible, and about the precise time at which a sighting is deemed valid.
When the crescent is obscured, the majority hold that thirty days must be completed. Thus, if the crescent of the month’s first night is hidden after the previous month has already lasted thirty days, the first of Ramadan is reckoned as the thirty-first day; and if the crescent of the last night is hidden, the people fast a full thirty days.
Ibn ʿUmar, however, maintained that if the crescent at the beginning of the month is concealed, the second day should be fasted—this is the so-called “Day of Doubt.”
Some of the early scholars reported that, when the crescent cannot be seen, one should resort to astronomical calculation of the courses of the moon and the sun; this was the view of Muṭarrif ibn al-Shikhkhīr, one of the eminent Successors.
Ibn Surayj relates that al-Shāfiʿī said: “Whoever follows astronomical inference by observing the stars and the moon’s stations, and by that method concludes that the crescent is in fact visible though hidden, may begin the fast, and it will suffice him.”