The believers are but a single brotherhood. Make peace and reconciliation between your two (contending) brothers and fear God so that you may receive mercy Quran 49-10.
As for those who divide their religion and break up into sects, you have no part in them in the least: their affair is with God. He will in the end, tell them the truth of all that they did Quran 6-159.
Other related Ayes in Quran:
3-102 3-105 6-65 6-159 8-45 8-62
9-10 30-31 42-13 49-9
The utmost important duty for every Muslim is to preserve and protect the Muslim unity and not to cause any division in the Muslim rank.
Islam was started by Prophet Noah and Abraham and was completed by Prophet Muhammad (PBUH).
All Muslims are brothers and equal with each other in the sight of God.
Islam and Race: All races are equal in Islam; black, white, yellow, red, or any combination of that.
Islam and Sect: Islam is a din (way of life). No division or sect is permitted by God (Quran 6-159), but Muslims have chosen various Imam's to follow. For example, Sonni's are either Shafi, Hanbali or Wahabi, etc. Sheas are either 12 Emami or 7 Emami, etc.
For the sake of Muslim unity all sects are acceptable and equal and we should learn to tolerate each other, different sects are just different flavors of the same principle.
Islam and national of origin: Islam has spread all over the world in more than 50 countries. Muslims are the majority of the population.
For sake of Muslim unity, national of origin should not become a source for division.
Islamic unity dictates that Muslims should not be divided according to race, sects or national of origin.
Q: What should we do during prayer about hands up or down, amin loud or silent, etc.?
A: During the group prayer, please follow the Imam. In private, either position is acceptable. Please do not discuss these issues in public it will only create more hostility and division among Muslim brothers.
Q: What about Islamic Centers for ethnic groups i.e., Pakistani mosque, Iranian mosque, or black Muslim's mosque.
A: All these divisions create hostility and contradict Muslim unity commanded by God in the Quran. The House of God should welcome all Muslim brothers and sisters regardless of race, sect or national origin.