Reference: Fataawa Ramadhaan – Volume 1, Page 167, Fatwa No.101
Fataawa ash-Shaykh Muhammad as-Saalih al-‘Uthaymeen – Volume 1, Page 476-477
Question: We heard the cannons tonight, (in Saudi Arabia, the cannons indicate the beginning and ending of Ramadhaan) more than once and we doubted whether or not it was ‘Eed or Ramadhaan so we waited until we heard something from the imaam before Fajr. But we didn’t hear anything. So what is the ruling regarding hesitancy towards whether to fast or not?
Response: It is obligatory upon a person to make verification and the basic rule (‘asl) is that things remain as they were. If there was something else it would have been openly clear so that the people would know and hence not take sahoor nor fast. In any case this day is considered as a day of Ramadhaan and if the ending of the month was established the matter would have been clear. So [based] upon this, it is obligatory upon the person to fast in such a situation without hesitancy. Because, the basic rule (‘asl) [in this case] is that Ramadhaan remains. If it became clear later on, that it was actually the day if ‘Eed he would break his fast.