There is a unanimous agreement amongst Ahl-us-Sunnah wal-Jamaa’ah that it is an obligation to stick to the Jamaa’ah  and that it is forbidden to break away from it, and that sticking to it is a virtue while separating oneself away from it is a vice.
Many evidences from the Qur’aan and the Sunnah, reaching the level of tawaatur, have been reported concerning this, and likewise there are many narrations from the Salaf with this regard. Allaah says:
“And hold onto the Rope of Allaah, all of you together, and be not divided…” [Surah Aali ‘Imraan: 103]
Ibn Abee Haatim  said: “My father narrated to me saying: ‘Amr Ibn ‘Alee As-Sairafee informed me, saying: ‘Abdu Rabbihi Ibn Baariq Al-Hanafee – and he praised him with good – narrated to me, saying: Simaak Ibn Al-Waleed Al-Hanafee narrated to me that he met Ibn ‘Abbaas in Madeenah and said:
‘What do you say about a ruler who governs us, yet oppresses and abuses us, shall we not prevent him?’
So Ibn ‘Abbaas said: ‘No, obey him, O Hanafee.’
And he said: ‘O Hanafee, the Jamaa’ah, the Jamaa’ah! Indeed, the nations that came before you were only destroyed because of their splitting up. Did you not hear Allaah say: ‘And hold onto the Rope of Allaah, all of you together, and be not divided…’”
Ibn ‘Atiyyah said in his Tafseer:
“The expressions of the scholars of Tafseer have varied with regard to the meaning of this (part of the) ayah ‘The Rope of Allaah.’ So Ibn Mas’ood said:
‘The Rope of Allaah is the Jamaa’ah.’
Anas Ibn Maalik narrated that the Prophet (صلى الله عليه و سلم) said:
‘Indeed, the tribe of Israa’eel split up into seventy-one sects. And my ummah (nation) will split up into seventy-two sects – all of them will be in the Hellfire except one.’
So it was said to him: ‘O Messenger of Allaah (صلى الله عليه و سلم), which is this (saved) one?’
So he (صلى الله عليه و سلم) clenched his fist and said: ‘The Jamaa’ah.’
Then he recited the ayah: ‘And hold onto the Rope of Allaah, all of you together.’
Ibn Mas’ood said in one of his khutbahs:
‘All of you together, adhere to obedience (of Allaah) and the Jamaa’ah, for indeed it is the Rope of Allaah that He has commanded us with.’
‘The Rope of Allaah that He commanded us to hold onto is the Qur’aan.’
‘The Rope of Allaah refers to the Book of Allaah.’
Ibn Mas’ood and Ad-Dahhaak also said this. And other things have been said, all of which are similar to what has been mentioned.
The word jamee’an (all of you together) is connected to the command ‘Itasimoo (Hold onto), so the meaning becomes: ‘Be united upon your mutual holding of it (the Rope of Allaah).’
‘And be not divided’ refers to the kind of division that leads to not uniting for Jihaad and for protecting the Religion and the Word of Allaah. This is the dividing that comes from tribulations (fitan) and dividing in matters of Creed.” [End of Ibn ‘Atiyyah’s words, rahimahullaah]
I say that their differing on the tafseer of the part of the verse: “Rope of Allaah” is a differing indicating variety in meaning, not a contradiction in meaning, as has been indicated here by Ibn ‘Atiyyah, Ibn ‘Abdil-Barr and other muhaqqiqeen. And his interpreting it to be the Book of Allaah combines all of the mentioned statements (of the Salaf). 
Al-Qurtubee mentioned in his Tafseer the opinion of those who say that the “Rope of Allaah” means the Qur’aan and the opinion of those who say it means the Jamaa’ah. Then he said: “The intended meanings are all close and similar for indeed Allaah commands unity and forbids division. This is since division is destruction while the Jamaa’ah is salvation.”
Shaikh-ul-Islaam Ibn Taimiyyah said:
“The ‘Rope of Allaah’ has been interpreted as Allaah’s Book (i.e. the Qur’aan), His Religion, Islaam, Sincerity, His Command, His covenant, Obedience to Him and as the Jamaa’ah. All of these sayings have been stated by the Companions and those who followed them in goodness until the Day of Judgement. And all of it is correct, for the Qur’aan commands towards the Religion of Islaam – and this is Allaah’s Command, His covenant and obedience to Him. And adhering to it jamee’an (in a unified group) can only be done with the Jamaa’ah. And the Religion of Islaam in reality is Sincerity to Allaah.” 
By this, it is understood that their sayings (i.e. of the Salaf) in their interpretation of “The Rope of Allaah” are not contradictory of one another but rather each saying compliments the other such that Allaah’s intended meaning becomes clear.
Ibn Jareer At-Tabaree reported in his Tafseer  that Qataadah said concerning the ayah:
“And do not be divided – and remember Allaah’s blessing on you.”
“Verily, Allaah hates that you be divided – and He forbade you from it. And He loves that you hear and obey and (stick to) the Jamaa’ah. So love for yourselves what Allaah loves for you – if you are able. And there is no might except by (the leave of) Allaah.”
 Translator’s Note: The Jamaa’ah refers to a collective body of Muslims upon the truth or upon a true state of affairs.
 Tafseer Ibn Abee Haatim (2/455) and in its chain of narration is ‘Abd Rabbihi Ibn Baariq Al-Hanafee. Al-Haafidh Ibn Hajr said of him: “He is honest but made mistakes (in narration).”
 Al-Muharrar Al-Wajeez fee Tafseer Al-Kitaab-il-‘Azeez (3/182) [Printed by Al-Maghrib]
 Reported by Ibn Jareer in his Tafseer (4/32), Ibn Abee Haatim in his Tafseer (2/452-453) from the path of Yazeed Ar-Raqaashee on Anas and its chain is weak. This hadeeth has been reported from numerous paths on the authority of Anas and others. All of them add strength to one another, except that there is not found in any of their wordings mention of this ayah besides this present narration of Anas, according to what I am aware of.
 They are six statements which Ibn Al-Jawzee has mentioned in his Tafseer Zaad Al-Maseer (1/432) [Printed by Al-Maktab Al-Islaamee]
 Al-Jaami’ Li-Ahkaam-il-Qur’aan (4/159) [Printed by Dar Al-Kutub]
 Minhaaj As-Sunnah (5/134) [Printed by Jaam’iah Al-Imaam Muhammad Ibn Sa’ood Al-Islaamiyyah]
 Jaami’ Al-Bayaan ‘an Ta’weel Ayy-il-Qur’aan (4/32)
Source: Shayks’s book “Al-Amr Bi-Luzoom Jamaa’at-il-Muslimeen” (pg. 7-11)
Translator: isma’eel alarcon