What is the ruling on one who fasts based on the sighting in his own country, then travels to a country with a different moon sighting?

Question : Honorable Shaykh, the questioner says: What is the ruling on one who fasted based on the sighting in his country, then arrived in the Kingdom? Does he break his fast when the people of the Kingdom break their fast? Or is he required to continue fasting until he returns to his country?

Answer : If a person arrives in a country, the ruling of that country regarding fasting and breaking the fast is required of him. For example, if he is from outside Saudi Arabia and arrives in the country, meaning Saudi Arabia, and the entry of the month is established there, he must fast, even if its entry was not established in his original country. Likewise, if the entry of the month of Shawwal is established in Saudi Arabia while he is in Saudi Arabia, he must break his fast, even if he did not see the crescent in his original country. In other words, a person follows the country in which he is when the crescent is established, due to the generality of the saying of the Messenger (peace and blessings be upon him): "Fast when you see it, and break your fast when you see it." However, if the month is short such that this man would only fast twenty-eight days, he is required to complete twenty-nine. For example, if the sighting of the month was established in one country on a Thursday, but was not established in the second country until the night of Saturday, and he arrived in the first country. If the first country, where the sighting was established on Thursday, establishes the sighting of Shawwal on the night of Saturday, how many days will this man have fasted? Twenty-eight days. At that point, he is required to make up one day, because the month does not fall below twenty-nine days.