Wa `alaykum As-Salamu wa Rahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
Dear brother in Islam, we are impressed by your question, which shows how concerned you are to abide by the Shari`ah in all details of your life. May Allah help us all lead a righteous life based on Islam!
First of all, we'd like to state that Muslims should strive their best to be united in all aspects, not only in the beginning and end of Ramadan and celebrating the `Eids. It is against the spirit of Islam to see Muslims in the same country divided in their rituals and their Islamic dates and events. The Islamic spirit is against 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, ought 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.
In this regard, the eminent Muslim scholar Sheikh Yusuf Al-Qaradawi states:
We should strive to achieve the unity of Muslims regarding the beginning and end of fasting and all other rituals. We should not lose hope in achieving this goal or removing the obstacles in its way.
However, it is to be stressed that if we fail to achieve the unity of the whole Muslim nation, we should at least be keen to achieve the unity of Muslims in each country.
It is agreed upon that the decision of the ruler or the people in authority and charge of Muslim affairs lifts the differences in disputable matters. Therefore, if the authority in charge of ascertaining the sighting of the moon in a given country (such as Dar al-Iftaa [House of Fatwa], Supreme Court, or Presidency of Religious Affairs) announces the sighting of the new moon, then Muslims in the region should follow its decisions, as it is obedience in goodness even if the decision differs with other countries.
In light of the above mentioned facts, Muslims are to be unified among themselves. They are to follow their own recognized authorities in order to achieve this goal. It is also the duty of Muslim organizations to reach an agreement on this issue in order not to cause disunity and division among Muslims.
Focusing more on the question of `Eid Al-Adha, Sheikh Faisal Mawlawi, Deputy Chairman of the European Council for Fatwa and Research, 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.