The default is that the Muslim fasts with the people of his country

Question:
Regarding the confirmation of the sighting of the Ramadan crescent last year, we heard of its confirmation through an Arab radio station, and we fasted based on that, but our country's radio station did not broadcast it, and a disagreement occurred among the people. Some said: This day is considered a day of doubt. Question: Is a person obligated, or bound, by his country, and by the sighting in his country, or by the sighting in any Islamic country? May Allah reward you with good.

Answer:
Fasting with the people of his country is more preferable; out of caution against disagreement and discord, since he fasts with them and breaks his fast with them if they are fasting in the Sharia-compliant manner, and they are seeking the sighting of the crescent; so his fasting with them and breaking his fast with them is more preferable; to avoid disagreement and out of caution against schism.
As for if they do not care; then it is by the sighting, if the sighting is established in any country as a Sharia-compliant sighting... an Islamic country, they fast by it; due to the saying of the Prophet (peace and blessings be upon him): If the state rules by the Sharia in that matter, and cares about the sighting; then they fast by its sighting, and praise be to Allah.
But if the people of his country care, and fast by the sighting, and break their fast, then he is with them, he does not separate from them, and he does not cause fitnah, rather he is with them in fasting and breaking the fast, for what is established from Ibn Abbas (may Allah be pleased with them both) that his mawla Kuraib came to him from Sham, and Ibn Abbas was in Madinah So he asked Kuraib about the fasting of the people of Sham? So Kuraib said: They fasted on Friday, they saw it on Friday so they fasted, and Mu'awiyah fasted. So Ibn Abbas (may Allah be pleased with them both) said: But we saw it on Saturday, so we will continue to fast until we see it, or we complete the number, thus we were commanded by the Messenger (peace and blessings be upon him)» meaning by this his saying (peace and blessings be upon him): .
So Ibn Abbas made the fasting of the people of Madinah on Saturday more preferable than following Mu'awiyah, this is the proof of the one who said: For every people of a country is their sighting, for every people of a country is their sighting if they care about the Sharia, and care about the sighting, yes, and if the Muslim fasts for the fasting of the country that preceded him and saw the crescent, and that was established, if they fasted by their sighting; then it is more preferable for them; so that the word of the Muslims is one, and so that they agree on their great month, the month of Ramadan.
And if the people of his country are alone, and they fast by their sighting; he fasts with them, and there is no harm, due to his saying (peace and blessings be upon him): and the report of Ibn Abbas that preceded in his story with the people of Sham.
And the summary: that a person fasts with the people of his country, and breaks his fast with them; if they care about the sighting, and if he fasts with others if they do not care, and do not pay attention to the sighting; then this is what is obligatory for him; acting according to the Sunnah, but if they care about the sighting, and fast by the sighting, or by the number; then he fasts with them, and breaks his fast with them; out of caution against schism and division.
As for if they do not have care for the month, or they fast by calculation, no, then it is obligatory for him to fast with those who fasted by the sighting; due to the saying of the Prophet (peace and blessings be upon him): Yes.

The presenter: May Allah reward you with good.