Abu Dawud

Benefits and Issues:
The intent of Ibn Abbas (radi Allahu anhu) is that for the people of every region, their own sighting (of the moon) is to be considered valid.
Imam Shafi'i (rahimahullah) further states regarding this that if the horizon (matla‘) of different regions is the same, then the sighting of one is valid for the others as well; otherwise, it is not.
This is also the position of Imam Ibn Taymiyyah (rahimahullah).

(1) “This is what has been commanded”—that you should begin fasting upon sighting the crescent moon and celebrate Eid upon sighting the crescent moon. This does not mean that every individual must sight the moon themselves; rather, if even a single trustworthy person sights the moon, or if news of the moon being sighted in another place reaches, then all the people of that region will fast or celebrate Eid, and the new month will commence. However, it is necessary to ascertain that the distance between the two places is not so great that it could result in a difference of one or two days in moon sighting. In the area where the moon has been sighted, the sighting will be considered valid for all the surrounding regions where the moon could also be seen. In this matter, guidance should be sought from scholars of astronomy. Nowadays, every Islamic country is so small that if the moon is sighted anywhere within the country, it can be seen throughout the entire country; therefore, if the moon is sighted in any part of a country, fasting or Eid can be observed throughout the whole country. However, the moon may differ between different countries; for example, Saudi Arabia and Pakistan are quite distant from each other. In this matter, only scholars of astronomy and celestial observation can make the correct decision; therefore, their participation in the moon sighting committee is extremely necessary. There are a few established principles in this regard:
➊ When the moon is sighted in one city, it will also be present in all cities located on similar longitudes, even if the distance between them is thousands of miles.
➋ If the moon is sighted in a city, then in all areas to its west, the moon will certainly be visible, and there is no need to sight it separately, even if the distance is thousands of miles. However, the reverse is not necessary; that is, the moon sighted in the west is not valid for the east, and it must be sighted separately.
➌ If the moon is sighted in an elevated area, it is not necessary that it will be visible in the lower area; however, the reverse is necessary, meaning if the moon is sighted in a lower area, then it will certainly be present in the elevated area. These principles are self-evident and there can be no disagreement in them.

(2) Although there is a considerable distance between Madinah Munawwarah and Damascus, in terms of longitude there is only a difference of six degrees. That is, there is a difference of 24 minutes in sunrise and sunset, and such a difference does not affect the sighting of the moon. The moon should be the same in both places on the same day. However, in that era, due to the lack of rapid means of communication, it was impossible for news to reach over such a distance in a timely manner. Therefore, Ibn Abbas radi Allahu anhu did not consider the sighting of the moon in Shaam (i.e., Damascus, which was the capital at that time) as sufficient for Madinah Munawwarah.

Hadith Commentary: Benefits and Issues: ➊
There is a difference of opinion among the Imams regarding the sighting of the crescent moon: if the moon is sighted in one region, what should the people of other regions do? ➊
If the supreme Imam, that is, the leader or ruler, accepts the sighting, then everyone must fast; otherwise, only the people of the place where it was sighted will fast.
➋
Each region has its own sighting.
➌
If the moon is sighted in one region, then people everywhere must take it into account.
➍
Consideration is given to the difference in horizons (ikhtilaf al-matali‘).
The regions that share the same horizon—
if it is sighted in one area, it should have been sighted in the other as well.
If it was not sighted due to some reason or impediment,
then for those sharing the same horizon, mutual sighting is preferable.
This is the position of the Iraqis and Imam Nawawi rahimahullah, and this is the correct view.
If the horizons are different, then sighting in one place does not necessitate sighting in another.
Therefore, the sighting in one place is not valid for another place.
➎
All areas of a province or a country have the same ruling.
➏
And according to Nawawi rahimahullah, Ghazali, and others, consideration is given to the distance of travel (masafat al-qasr); if the distance is less than the distance of shortening prayers (masafat al-qasr), then the ruling is the same, otherwise, it is different.

➋
In the present era, the announcement of the crescent sighting committee is considered valid; if they make an announcement after taking testimony according to the Shari‘ah principles, it will be accepted.

➌
It is stated that the position of Imam Abu Hanifah rahimahullah, Imam Malik rahimahullah, Imam Ahmad, Layth ibn Sa‘d rahimahullah, and some Shafi‘is rahimahullah is that:
“(Fast upon its sighting and break the fast upon its sighting)”
The command to fast upon sighting the moon and to end the fast upon sighting it
is general and addresses all Muslims.
Thus, it would mean that the beginning and end of fasting should be the same in all Muslim countries, and the lunar date should be nearly the same everywhere, although in reality, this is not possible.
On the other hand, there is consensus that if the distance between places is extraordinary, such as between Hijaz and Andalusia, then their rulings are separate.
(Bidayat al-Mujtahid, vol. 1)

➍
For the crescent of Ramadan, the testimony of one person is sufficient according to most scholars.
And for the crescent of Shawwal, the testimony of two men is valid according to the four Imams rahimahullah.
However, Qadi Shawkani rahimahullah has supported the position of Imam Abu Thawr rahimahullah that for Shawwal as well, one testimony is sufficient, just as in Ramadan.