Someone fasted today then found out just now that his masjid is doing Eid (in Maryland). What should he do?
بِسْمِ اللهِ الرَّحْمنِ الرَّحِيْم
In the name of Allah, the Most Gracious, the Most Merciful
If one is fasting and later it has become established from your local scholars and jurists that the moon has indeed been sighted, then one must break his fast. If the announcement is made before zawaal, one may also pray eid prayer, and if for some reason the time for zawaal has passed (due to late announcement etc.) then one can pray on the following day.
A similar incident took place in the time of the Holy Prophet s.a.w.
It has been narrated by Umair bin anas who narrates from a number of sahabah that a caravan came and testified that they had seen the moon the previous day, therefore, the Holy Prophet s.a.w ordered them to break their fast and to pray Eid salah the following day.
Only Allah knows best
Written by Maulana Belaal Ahmed
Checked and approved by Mufti Mohammed Tosir Miah
Darul Ifta Birmingham
 Fataawa Mahmoodiya vol 8 pg 375