Sighting of the New Moon

According to the majority of scholars, it does not matter if the new moon has been sighted in a different location. In other words, after the new moon is seen anywhere in the world, it becomes obligatory for all Muslims to begin fasting, as the Prophet said: "Fast due to its sighting and break the fast due to its sighting." This hadith is a general address directed to the whole Muslim world - that is, "if any one of you sees the moon in any place, then that will be a sighting for all of the people." 

- Fiqh us-Sunnah V.3