Firstly, it should be noted here that Muslims should do their best to be united in all aspects of life. It is against the spirit of Islam to see Muslims in the same country divided in their rituals and their Islamic dates and events. Islam calls to unity and consolidation and condemns division and disunity. That is why Muslims are not allowed to hold two congregational prayers in one mosque at the same time.
Muslim scholars have differed regarding the following issue: if the new moon is sighted in one region or country, should the people of other regions follow this sighting or follow their own sighting? The preferable view is that Muslims in other regions and countries are to follow this sighting as long as these countries share one part of the night.
However, if this unity cannot be achieved nowadays, then Muslims in each country must be united on celebrating the Islamic occasions and rituals. The dilemma of Muslims in the West is that they are divided between their locality and their countries of origin. Some are inclined to follow their countries of origin or major Muslim centers like Saudi Arabia. This, in fact, causes division among Muslims living in the West and they fail to achieve the least level of unity regarding their Islamic dates and events. Moreover, this causes Muslims problems with the authorities in these countries and deprives them from some of their rights. For instance, Muslims cannot demand the day of `Eid as a day off if they do not agree on a certain day.
Focusing more on this issue of `Eid Al-Adha, Sheikh Faisal Mawlawi states:
“Difference among Muslim countries in the beginning and end of Ramadan may be passable, though it’s better—according to the majority of Muslim scholars—to unite all Muslims in this aspect.
`As for Eid Al-Adha, difference among Muslim countries is not passable at all, for Muslims should follow the occasion of Hajj. Therefore, the Day of `Arafah is the Day when pilgrims stand on the mountain of `Arafah, and Muslims should celebrate the same day with them. Sighting the moon of Dhul-Hijjah carries no weight in other countries if it differs from that of Saudi Arabia.
This is my opinion in this regard, but I cannot force all people to follow it. Celebrating `Eid Al-Adha in accordance with Saudi Arabia—the place of Hajj—carries more weight.”