The following question is answered by Shaikh Saalih bin Fawzaan Al-Fawzaan and taken from the book, Beneficial Answers to Questions on Innovated Methodologies, Compiled and Commented by Jamaal bin Furayhaan Al-Haarithee.
Question: What are the means and ways of achieving unity?
Answer: The means of achieving unity are:
First: Correcting one’s Creed, such that it becomes purified from Shirk. Allaah says:
“Verily this nation of yours is one (unified) nation, and I am your Lord, so be dutiful to Me.” [Surah Al-Mu'minoon (23):52]
It is only the correct creed that will unite the hearts and vanquish the malice, as opposed to there being various beliefs and several deities, for each adherent of a creed will incline towards his own creed and deity, whilst holding that which others are upon to be falsehood. This is why Allaah says:
“Are many different lords (i.e. gods) better or Allaah, the One, the Irresistible?” [Surah Yoosuf (12):39]
This is the reason why the pagan Arabs in the Days of Ignorance were divided and suppressed in the earth. However, when they entered into Islaam and their creed and beliefs became rectified, they united their ranks and unified their rule.
Second: Hearing and obeying the Muslim rulers, which is why the Prophet (صلى الله عليه وسلم) said:
“I counsel you to have Taqwaa (fear/obedience) of Allaah, and to hear and obey (the rulers) even if an Abyssinian slave assumes leadership over you, for indeed whoever lives (long) amongst you will see great differing…”
[Saheeh: Reported by Abu Dawood (4607), At-Tirmidhee (2776) and al-Haakim (1/96), and the wording here is from his report]
Disobeying the Muslim ruler leads to differing.
Third: Returning back to the Qur’aan and the Sunnah to quell disputes and end differing. Allaah says:
“So if you differ in some matter, then return it back to Allaah and His Messenger, if you truly believe in Allaah and the Last Day. That is better and more suitable for final determination.” [Surah An-Nisaa (4):59]
One should not turn back to the opinions and traditions of men.
Fourth: Rectifying and reconciling, when disputes occur, between individuals or nations. Allaah says:
“So fear Allaah and rectify all matters of dispute between you.” [Surah Al-Anfaal (8):1]
Fifth: Fighting the transgressors and renegades who seek to split the unity of the Muslims. If they are strong and powerful, they will demolish the Muslim society and corrupt the ummah. Allaah says:
“But if one of them transgresses against the other, then fight against the one that transgresses.” [Surah Al-Hujuraat (49):9]
This is why the Commander of the Believers, ‘Alee bin Abee Taalib (رضي الله عنه), fought against the transgressors and Khawaarij. And this was considered one of the greatest of his virtues.