What is the ruling for a person who began his fast in one country and then traveled to another where the people fasted one day before or after his home country?

Commenting on Imam Al-Nawawi’s words in his famous book Al-Minhaj, Sheikh Al-Ramli said that whoever travels from a country in which the new crescent has not been sighted to another country in which it has, and breaks his fast with the latter i.e. he has fasted twenty-eight days and celebrated ‘Eid on the twenty-ninth, must make up a fast-day because a lunar month is never twenty-eight days. But if he has fasted twenty-nine days nothing is required from him because it is possible for a lunar month to be twenty-nine days.

For this reason, a traveler must follow the moon sighting of the country of his destination. If the number of days he has fasted is less than twenty-nine, he should fast an extra day after breaking his fast for the ‘Eid celebration. But if he has fasted thirty days and finds that the people in the country he has traveled to are still fasting, he should refrain from breaking his fast in front of others (as the lunar month never exceeds thirty days and is never less than twenty-nine days). By this, he should intend not to harm or bother his fellow Muslims and to prevent unrest among the people who are ignorant of religious legal rulings.

And God Almighty knows best