The month may consist of twenty-nine nights. So do not fast till you have sighted it (the new moon) and do not break it till you have sighted it, except when the sky is cloudy for you, and if it is so, then calculate it.
The Book of Fasting - Sahih Muslim 1080 h
In the name of Allah, the Most Gracious, the Most Merciful. This noble hadith from Sahih Muslim establishes the fundamental principles governing the commencement and conclusion of the blessed month of Ramadan.
Lunar Month Determination
The Prophet (peace be upon him) informs us that the lunar month may be twenty-nine days, emphasizing the variability of the Islamic calendar which follows the natural lunar cycle rather than fixed calculations.
This teaching preserves the original method of moon sighting as established in the Shariah, maintaining the connection between worship and celestial observation.
Visual Moon Sighting Requirement
"Do not fast till you have sighted it" establishes that Ramadan begins only upon verified visual sighting of the crescent moon after the 29th of Sha'ban.
Similarly, "do not break it till you have sighted it" means Eid al-Fitr occurs only after sighting the Shawwal moon, completing thirty days of fasting if the moon is not visible.
Cloudy Sky Provision
The exception "when the sky is cloudy" provides practical guidance for situations where visual sighting is impossible due to weather conditions.
"Then calculate it" means to complete thirty days of the previous month, as explained by classical scholars including Imam Nawawi who stated this means to complete Sha'ban as thirty days when clouds prevent moon sighting.
Scholarly Consensus
The majority of classical scholars, including the four madhabs, agree that actual moon sighting takes precedence over astronomical calculations for beginning and ending Ramadan.
This hadith forms the basis for the unified practice of Muslim communities worldwide in determining the sacred months, preserving the Sunnah while allowing for necessary accommodations in exceptional circumstances.