Allah's Messenger (ﷺ) mentioned Ramadan and said, "Do not fast unless you see the crescent (of Ramadan), and do not give up fasting till you see the crescent (of Shawwal), but if the sky is overcast (if you cannot see it), then act on estimation (i.e. count Sha'ban as 30 days).
The Prohibition of Premature Fasting
The Prophet (ﷺ) forbade initiating the Ramadan fast before the confirmed sighting of the crescent moon. This establishes that fasting is a time-bound worship whose commencement depends on visual evidence, not calculation or assumption.
The Lunar Sighting Principle
The command to "see the crescent" emphasizes the physical sighting as the primary means of establishing Ramadan's beginning. This method preserves the Ummah's unity under a single visible sign, making the obligation accessible to all Muslims regardless of scholarly knowledge.
Scholars interpret "seeing" to include verified reports from trustworthy witnesses, not merely personal sighting. The testimony of one just Muslim is sufficient according to the majority position.
Completion of the Fast
The instruction to continue fasting until the Shawwal crescent is sighted prevents premature celebration of Eid. This ensures complete fulfillment of the Ramadan obligation—either 29 or 30 days as determined by the lunar cycle.
The Overcast Sky Provision
When clouds prevent crescent sighting, the command to "act on estimation" means completing the previous month (Sha'ban) as 30 days. This practical solution prevents uncertainty and maintains the lunar calendar's integrity.
Scholars derive from this that 30 days should be completed for Sha'ban when the Ramadan crescent isn't sighted due to weather conditions, ensuring Ramadan begins on a definite date.
Legal Wisdom and Unity
This hadith establishes the principle of visual moon sighting over astronomical calculations for communal acts of worship. It preserves the simplicity of Islamic law while ensuring the Ummah's unity in observing these important occasions together.