for anyone to base his fasting and breaking the fast on such calculations, thereby dispensing with observing the crescents, according to scholarly consensus. The Messenger of Allah (peace and blessings be upon him) said concerning Ramadan:

“Fast when you sight it, and end the fast when you sight it. If it is obscured from you, complete the count as thirty days.”

The scholars differed only over whether someone versed in this subject may rely on his own knowledge when the crescent is obscured, in light of the Messenger of Allah’s saying (peace and blessings be upon him): “If it is obscured from you, estimate it.” Mutarrif ibn ‘Abd Allāh ibn al-Shikhkhīr held that such a person may rely on this for his own observance. This was also the view of al-Shāfi‘ī according to one report, although his established position agrees with the majority: such calculations are not to be relied upon.

The scholars differed over the meaning of the Prophet’s words (peace and blessings be upon him), “Estimate it.” Mālik held that his words (peace and blessings be upon him) in the second hadith, “Complete the count as thirty days,” explain them. Al-Tahāwī held that the second hadith abrogates the first. He further held that, before its abrogation, estimating meant observing when the moon set on the second night if the crescent had been obscured on the night of doubt. If it set after the interval corresponding to one lunar station—six sevenths of an hour—they would know that the month began that night. If it set after two stations—one hour and five sevenths—they would know that the month had begun the previous night, and would make up that day’s fast.

This view is plainly mistaken. The moon does not set six sevenths of an hour after nightfall every night of every month, whether the month is short or full. This is known with certainty from observing that, at the beginning of the months, some crescents are higher and set later than others. Moreover, this contradicts the apparent meaning and import of the hadith: the estimation was commanded at the outset, before the opportunity had passed, so that one could fast or end the fast—not afterwards, once it had passed, to determine whether or not one should make up the fast.

My view concerning the estimation commanded in the hadith when the crescent is obscured is that one should examine the months preceding the month at whose end the crescent has been obscured. If two or three consecutive months had been full, one should treat the current month as short, and the people should begin the next morning fasting,