Subannallah May be this can help us, I got this information from a daw'wah brochure on Ramadhan.
An Islamic day/date begins at sunset and ends at the following sunset. The Islamic month begins from the first day/date determined by the 'crescent's seen after sunset and ends with the next month's crescent. Logically, the Hilal (a crescent seen after sunset) is the only criterion for an Islamic lunar calendar. This is based on a decree from Allah.
They ask you about the crescents. Tell (them) they are for fixing time for men and the Hajj. (2:198)
For centuries the Muslims followed the simple rule of going out on the 29th evening and watching for the crescent. If it was seen, then well and good; if not, then the month was completed to 30 days. This was based on explicit instructions from the Messenger of Allah (Peace and Blessings be upon Him).
Abu-Haurayrah (May Allah be pleased with him) said that Allah's Messenger( peace and Blessings be upon him) said; When ever you sight the crescent (of the month of Ramadhan) observe fast, and when you sight it (the crescent of Shawwal) break it, and if the sky is cloudy for you, then observe fast for thirty days. (Sahih Muslim Hadith 2378; Sahih Bukhari Vol3:133)
The statement of the Prophet (peace and Blessings be upon him) "Start fasting on seeing the (Hilala) crescent of (Ramadhan), and stop fasting on seeing the (Hilala) crescent of (Shawwal)". And Ammar (May Allah be pleased with him) said; "Who ever fasts on a doubtful day is disobeying Abu-Qasim". (Sahih Bukhari Vol.3 chapter 11)
