Ibn ‘Umar reported God’s messenger as saying, “Do not fast till you see the new moon, and do not break your fast till you see it; but if the weather is cloudy calculate when it should appear.” In a version he said, “The month consists of twenty-nine days, but do not fast till you see it, and if the weather is cloudy wait till thirty days of the previous month have passed.” (Bukhari and Muslim.)
The Lunar Sighting Principle
This noble hadith establishes the fundamental methodology for determining the commencement and conclusion of Ramadan, the month of fasting. The Prophet (peace be upon him) explicitly linked the act of fasting to the physical sighting of the new crescent moon (hilal), thereby grounding this act of worship in a tangible, empirical reality. This instruction serves to unify the Muslim community upon a single, observable phenomenon, preventing division and speculation.
The Command and Prohibition
The phrases "Do not fast till you see the new moon" and "do not break your fast till you see it" are clear legal injunctions (ahkam). The prohibition against beginning the fast before the moon is sighted protects the sanctity of the prescribed time, ensuring that worship is performed exactly as legislated by the Divine Lawgiver. Similarly, the prohibition against ending the fast prematurely preserves the completeness of the act of devotion.
The Case of Cloudy Weather
The instruction, "but if the weather is cloudy calculate when it should appear," provides the solution for a common practical difficulty. The scholars (ulama) have explained this "calculation" (faqduru lahu) to mean completing the previous month of Sha'ban to thirty days. This is based on the other version of the hadith which clarifies it as, "wait till thirty days of the previous month have passed." This principle, known as 'istikmal' (completion), is a safe and certain method prescribed by the Shari'ah when direct sighting is obstructed.
The Month's Natural Duration
The Prophet's statement, "The month consists of twenty-nine days," affirms the natural, lunar-based reality. A lunar month is either 29 or 30 days, and it is never more. This negates any possibility of a month having 31 days in the Islamic calendar. The instruction to wait for thirty days only applies when the moon is not sighted on the 29th, thereby confirming that the month has reached its full, alternate duration.
Scholarly Consensus and Application
The majority of the classical scholars held that the physical sighting of the moon by trustworthy Muslim witnesses is the primary means for establishing the months of Ramadan and Shawwal. The command is directed at the community as a whole; once a reliable sighting is confirmed by the authorities, it becomes binding upon all. This hadith, found in the esteemed collections of Al-Bukhari and Muslim and referenced in Mishkat al-Masabih 1969, forms the cornerstone of the Islamic legal chapter on Fasting.