Tell me in detail about the concept of brotherhood in Islam with the references of Qur'an and Sunnah.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

Imaam Al-Gazaali said: "Loving for the Sake of Allaah and the ties of brotherhood which are established on the basis of religion, are among the most important acts that bring a person closer to Allaah. Generally they are practised as common habits but one may change them to good forms of worship if one fulfills the conditions and then becomes among those who love and befriend for the Sake of Allaah. This relationship has some rights, by fulfilling them, one gets closer to Allaah in position, and by regularly observing them, one reaches the highest degrees.

He also said: "Intimacy is the result of good morals while disunity is the result of bad morals. So, good morals lead to love and affection while bad bad conduct leads to hatred, envy and discord." 

There are many Ahadeeth that prove the virtues of brotherhood for the Sake of Allaah among which are the following:

- Anas narrated that the Prophet said: "If a person has the three following qualities he will indeed find the sweetness of faith: If he loves Allaah and His Messenger more than anyone or anything else, and he loves a person only for the Sake of Allaah, and he hates to go back to disbelief after Allaah had saved him from it in the same manner as he hates to be thrown into Hellfire." [Al-Bukhari and Muslim]

- Abu Hurayrah narrated that the Prophet said: "Verily, Allaah would say on the Day of Resurrection: Where are those who love each other for My Sake?"; today I shall shelter them under My Shade when there is no other shade but My Shade." [Muslim]

- Abu Hurayrah also narrated that the Prophet said: "Allaah will give shade to seven kind of people on the Day when there will be no shade but His. He mentioned among those two men who loved each other for Allaah's Sake only  and they met and departed (from each other) for Allaah's Sake." [Al-Bukhari and Muslim]

- Abdullaah Ibn 'Umar narrated that the Prophet said: "The best companion in the Sight of Allaah is the one who is best to his companion and the best neighbor in the Sight of Allaah is the one who is best to his neighbors." [Al-Tirmithi, Ibn Khuzaymah, Ibn Hibbaan and Al-Haakim who said that it is authentic according to the conditions set by Muslim]

- There is another Hadeeth reported by Abu Ad-Dardaa' that the Prophet that the Prophet said: "If two men love each other for the Sake of Allaah while they are absent (from each other); the most dearer to Allaah is the one who has much love for his companion."  [Al-Munthiri said that it was reported by At-Tabaraani who graded it as good]

However, one should befriend the one who meets some qualities such as:

1.  He should be a wise person.  Al-Gazaali said: "Sound mind is the capital of a person, and it is the principle; thus there is no benefit in befriending a foolish person; his friendship will ultimately come to an end it will lead to the cutting of relations.  'Ali composed some good poetry in this concern.  The translation is presented here.

"Do not befriend a foolish person; avoid him totally.  Many unwise persons have destroyed wise men when they befriended them.  A person is compared with the person with whom he socializes.  Indeed, a heart affects a heart when they meet."

2.  He should have good manners.  Al-Gazaali said in his book entitled Al-Ihyaa': "Good manners must be considered while befriending one because many wise people know the reality but when they are under the influence of anger, desire, stinginess or cowardliness, they submit themselves to their desires and oppose the known realities since they cannot control their lusts and cannot correct their manners."

3.  The person should safeguard the rights of his friend in his presence and absence.  Al-Gazaali said: "Some writers stated that one should not befriend except the one who keeps the secrets of his friend, conceals his shortcomings, supports him at hard times, prefers his necessities, spreads his good acts, and conceals the bad ones.  If one does not find such a person, then he should not befriend anyone. 'Ali said: "The true friend is the one who stands with you in your hard times, harms himself to benefit you and bears all kinds of calamities to protect you."

4. This is the most important quality, a friend should be a religious one, looking at him reminds of Allaah, sitting with him helps in the obedience of Allaah.  Al-Gazaali said: "There is no benefit in befriending a dissolute person who insists in his disoluteness, since the person who fears Allaah will not insist on committing major sins, whereas the one who does not fear Allaah, he is not a reliable person and his friendship is not trusted, as he changes according to the change of his interests. Allaah Says (what means): {…and obey not him whose heart We have made heedless of Our Remembrance, one who follows his own lusts…}[Quran 18:28]. Allaah also says: {Therefore withdraw (O Muhammad SAW) from him who turns away from Our Reminder (this Quran) and desires nothing but the life of this world.}[Quran 53:29]

Allaah also says: {…and follow the path of him who turns to Me in repentance and in obedience….} [Quran 31:15]

The verse indicates that one should not socialize with dissolute persons. As regards befriending an innovator, then this is very dangerous because the innovations may pass to him.  An innovator deserves to be deserted from all relations, so how can a person make friendship with him. 'Umar said: "You must choose good friends to live with because they are a source of pride in happiness and a source of help during calamities."

Nonetheless, a Muslim brother has some rights upon another Muslim brother which he should take into consideration, and they are as follows:

1. Responding to his greetings (answering his Salaam).

2. Visiting him when he is sick.

3. Accepting his invitation.

4. Saying to him "May Allaah have mercy upon you", when he sneezes and says "Alhamdu lillaah -Praise be to Allaah."

5. Following his funeral processions.

6. Giving him good advice.

All the above rights are mentioned in a Hadeeth narrated by Abu Hurayrah that the Prophet said: "A Muslim has six rights upon his fellow Muslim brother. The Companions said: "What are they, o Prophet of Allaah?" He [the Prophet] replied: "If you meet him, you should say Salaam to him, if he invites you, you should accept his invitation, if he seeks your advice, you should advise him, if he sneezes and says "Alhamdu lillaah -Praise be to Allaah.", you should say to him "May Allaah have mercy upon you", if he is sick, you should visit him, and if he dies,  you should follow his funeral procession." [Muslim]

7- To do what he makes on oath on you to do; Al-Baraa' said: "The Prophet ordered us to do seven matters and forbade us from doing seven. Among the matters he ordered us to do is doing what a brother swears on us to do." [Al-Bukhaaari]

8- One should like for his brother what he likes for his own self.  Anas narrated that the Prophet said: "None of you will really be a beleiver till he likes for his brother what he likes for his own self." [Al-Bukhari and Muslim]

9- Not causing harm to him. 'Abdullaah Ibn 'Amru narrated that the Prophet said: "A Muslim is he from whose hand and tongue the Muslims are safe." [Al-Bukhari and Muslim]

10- Behaving humbly and modestly with other Muslim brothers.  The Prophet said: "Allaah revealed to me that you should be humble amongst yourselves so that no one would act proudly towards another person, and no one should be unjust to anyone else." [Muslim]

11- One should not oppress another, as mentioned in the above Hadeeth.

12-  One should not forsake his brother when the latter expects from him support.  The Prophet  said: "Muslims are equal in respect of blood. The lowest of them is entitled to give protection on behalf of them.  They are like one hand against the enemy.  A believer should not be killed because of a non-Muslim, and a non-Muslim who is given protection in a given country should not be killed." [Ahmad, An-Nasaa'i and others]

There are many other rights mentioned in the Quran and the Sunnah.

Allaah Knows best.