And he (sawa) said...

And he (sawa) said: Do not stop fasting unless & until all thirty days are complete starting with sighting of the crescent (for the beginning of Ramadhan) or with the witnessing of two witnesses who sighted it (crescent of Shawwal).’ [^4] (Meaning: if the witnesses sighted the crescent of Shawwal earlier then you must stop fasting even if 30 days are not complete).

This is what could be understood from this hadith of the Holy Prophet (sawa): Suppose it is the 29th day of Ramadhan and two just (‘Adil) people inform the one who is fasting that they saw the crescent in the daytime, then this person should not break the fast. Now suppose one fasts for 30 days and still the moon was not sighted then he should not fast more than 30 days. Suppose the moon was sighted on the 29th day and the two just (‘Adil) people reported it, then he should not fast the 30th day.

In other words, this hadith of the Holy Prophet (sawa) that is found in Da’aimul Islam, clearly says that the starting and the ending of the month should be based on sighting of the crescent. We also learn from this hadith that Ramadhan could be less than 30 days.

[^6] The Ismailis and the Ithna Asharis both believe in Imam al-Baqir and Imam al-Sadiq (as).