The Crescent
Question :

We know that the beginning of the month should be proven by the testimony of two trustworthy witnesses that they saw the crescent. However, if a person saw the crescent himself alone, while nobody else had gone out to look for it, is he obligated to begin fasting? What if others have tried to see the crescent but did not see it?

Answer :

The beginning of the month is established by physically seeing the crescent, or by the testimony of two trustworthy witnesses, among other ways. If one was certain that he saw the crescent, then he must consider it the first of the month, in both mentioned cases.