Ruling on fasting and breaking the fast of one whose testimony was rejected or who was not able to inform the authorities
Question

                If a person sees the new moon of Ramadaan but could not tell the superiors or was not believed about seeing it, should he fast alone, and what about Eid? Should he break the fasting alone?.
Praise be to Allah.
    Some of the scholars are of the view that he should fast by 
    himself, but the correct view is that it is not permissible for him to fast 
    by himself or to break the fast by himself, rather he should fast with the 
    people and break the fast with them, because the Prophet  (peace and 
    blessings of Allaah be upon him) said: “The fast is the day when you 
    (plural) fast and the breaking of the fast is the day when you break the 
    fast.” But if he is in the wilderness and has no one with him, then he may 
    start and end the fast on the basis of his own moon sighting. End quote. 

    Shaykh ‘Abd al-‘Azeez ibn Baaz (may Allaah have mercy on him)