The believers are but a single brotherhood: So make peace and reconciliation between your two (contending) brothers; and fear God, that ye may receive Mercy. (49:10)
It also mentions:

And hold fast, all together, by the rope which God (stretches out for you), and be not divided among yourselves; and remember with gratitude God's favor on you; for ye were enemies and He joined your hearts in love, so that by His Grace, ye became brethren; and ye were on the brink of the pit of Fire, and He saved you from it. Thus doth God make His Signs clear to you: That ye may be guided. (3:103)
In a Hadith it has been related: In their love, kindness and compassion for each other, the believers are like a human body: when one part of it is hurt, the rests sympathizes with it in wakefulness and fever.1

2. Reflect on Hajj as a time for Muslim unity
Use this time personally, as well as within your family and community, to remind Muslims of how the Hajj is a unifying factor for Muslims. Hold a family meeting about the topic. Organize a seminar at your mosque about how Hajj is a beautiful symbol for Muslim unity. Make sure your speakers are those who have performed Hajj and can attest to this fact. Also, brainstorm practical ways the lessons of unity from Hajj can be learned in your community throughout the year and come up with an action-plan to implement them.
During the process of planning, make Du’a for unity throughout the period of the first ten days of Dhul Hijjah, which is a blessed time. Say the Masnun Takbirat (recommended glorifications) and add the Talbiyyah to it: Labbayk, Allahumma Labbayk, Labbayk, La Sharika Laka Labbayk, Inn Al-Hamda Wa Ni’mata Laka Wa Al-Mulk, La Sharika Laka (“O my Lord, Here I am at Your service, Here I am. There is no partner with You. Here I am. Truly, the praise and the provisions are Yours, and so is the dominion and sovereignty. There is no partner with youâ€‌).
Say it with your children and family and think about its meaning, remembering that you are at Allah’s service. You cannot serve Him unless you are united.

3. Learn tolerance towards other points of views
Is it not interesting that we can attend classes at college or speak with colleagues from work and discuss issues while being willing to disagree with them? But the minute some of us step into a mosque or a Muslim community function, all that tolerance seems to get thrown out the window.
Contrary to popular belief, Islam is a broad and extensive faith, and you can find a range of scholarly views on issues as diverse as how to place our hands during prayer to whether or not Muslims should participate in the American political process. If our scholars from the past and present have shown such tolerance towards differing views on the various issues, who are we, as average Muslims who do not have the same level of knowledge, to express intolerance towards another point of view?
To understand this point thoroughly, I would recommend Dr. Yusuf Al-Qaradawi’s book Islamic Awakening Between Rejection and Extremism.

4. Learn to criticize without injuring
The way some Muslims criticize each other, one would think they were talking to an enemy of Islam instead of a fellow brother or sister. This type of ignorant behavior is a sure way to create anger, hurt, and dissension. It is no route towards unity.
We must learn the proper Adab (etiquette) of criticism, whether it is towards individual Muslims or our leaders. Knowing and implementing this will not only help solve problems in a practical manner but will also lead to a greater sense of brother and sisterhood in the community.
If you feel that your criticism of someone in the past was rude or hurtful, pray for that brother or sister, since the Prophet has said that Du’a increases love between people, and return to them apologetically.

5. Avoid adopting harsh positions in trivial matters
There is what is called a “Fiqh of prioritiesâ€‌ and this essentially means that there are some aspects of Islam that are more important than others. For instance, it is more important to emphasize that Muslims establish prayer than whether or not there should be a curtain between men and women in mosques.
Knowing what our priorities are will help us avoid turning secondary issues of faith into factors of division in our communities. Muslim leaders, in particular, must not only understand this but implement it in their communities across North America so that small differences do not destroy the idea of Muslim unity.

6. Do not call anyone a Kafir
This horrible phenomena of calling fellow believers Kafirs must end if we want to create a climate that is conducive to unity. Kafir-calling is a sure way to isolate individuals from the Muslim community. We must remember that Muslims in North America come from all cultural and socio-economic backgrounds, whether they were born and raised in the faith or reverted to it. If a person is expressing ideas that are not in line with Islamic values, he or she must be gently corrected. Kafir-calling will only fuel their ignorance, anger and stubbornness, not to mention humiliate and embarrass them.
The Prophet warned that if one person calls another a Kafir and the person who is labelled as such is not a Kafir, the individual who made the accusation is considered a Kafir. Given this warning, is it not sad that there is an organization in Egypt which calls itself â€کthe Party of Declaring Others Kafirs’ (Jama’ah Al-Takfir Wa Al-Hijrah)?

7. Reaching out across ethnic boundaries
The ignorant practice of maintaining “ethno-centric mosquesâ€‌ is, Alhamdulillah, slowly but surely disappearing in North America. Nevertheless, there is still a long way to go. All of our institutions, functions, and communities in general must become more ethnically diverse and open to the needs and concerns of Muslims of all backgrounds. Muslim leaders and individuals have a duty to ensure that no Muslim, regardless of their ethno-cultural background, feels shut out of the community, ignored, or neglected.
This can only be done by Muslim leaders and individuals taking the first step and reaching out to Muslims who may have been traditionally isolated because of ethnocentricity in mosques and other institutions. It is not enough to just open the door to all. A direct effort has to be made to solicit feedback, advice, and support from all Muslims so that they feel a part of the community.
Another, more personal way of reaching out is to invite Muslims of diverse backgrounds to your home for food. Extend this invitation to non-Muslims as well to break barriers and share Islam.

8. Heed the advice found in Surah Hujurat
Chapter forty-nine of the Qu’ran provides excellent guidance on the kind of behaviour that Muslims should avoid in order to establish Muslim unity. For instance, Allah advises us to avoid mockery, defamation, and suspicion. These are all things which serve to divide communities and create hatred, hurt, and dissension.
Discuss the themes of Surah Hujurat relating to Muslim behaviour in family meetings, Khutbas (sermons), talks, study circles, and classes for young and old Muslims in your community to share this divine wisdom with all.
Whenever you recall that you have done Ghibah (backbiting) against a Muslim or non-Muslim, you should remember that you need to seek that person's forgiveness. Doing this is a prerequisite to washing off that sin.

9. Share these tips with a wider audience
Share the above-mentioned tips with fellow Muslims in your community. This can be by suggesting to the Khatib (preacher) of Friday and Eid prayers to use the topic of this article for his sermon. Or you can print it out and hand it to worshippers, or publish it in your local mosque newsletter. It is also important to discuss it in various Muslim settings to start the thinking and reflection process amongst Muslims.

10. Make Du’a for unity
Ask your Imam to emphasize unity as an Islamic duty in his Khutbahs and suggest practical ways it can be achieved in your country or Islamic organization. Also, encourage Muslims to go for Hajj and to make special Du’a for Muslim unity. When the Hajis (pilgrims) return from the pilgrimage, the Prophet has encouraged us to receive them and to request them to make Du’a. This is another opportunity to seek Du’as for Muslim unity. Finally, make sure that you as an individual are not only working for unity but making Du’a for it as well, since the end result of all actions are in Allah’s Hands.
1. Sahih Bukhari and Muslim.