In The Name of Allaah, The Most Merciful, The Bestower of Mercy.

Allaah [The Most High] said:

وَأَطِيعُواْ ٱللَّهَ وَرَسُولَهُ ۥ وَلَا تَنَـٰزَعُواْ فَتَفۡشَلُواْ وَتَذۡهَبَ رِيحُكُمۡ‌ۖ وَٱصۡبِرُوٓاْ‌ۚ إِنَّ ٱللَّهَ مَعَ ٱلصَّـٰبِرِينَ

And obey Allah and His Messenger, and do not dispute [with one another] lest you lose courage and your strength depart, and be patient. Surely, Allah is with those who are As-Saabireen [the patient ones, etc.]. [Surah Al-Anfaal Ayah 46]

[وَأَطِيعُواْ ٱللَّهَ وَرَسُولَهُ ۥ – And obey Allah and His Messenger]: Meaning: obey Allaah and the Messenger in that which you have been commanded, [and keep away from everything forbidden by Allaah and His Messenger], and adhere to this path in all circumstances. [وَلَا تَنَـٰزَعُواْ – and do not dispute (with one another)]: Meaning: Do not dispute because it will cause your hearts to become disunited; [Ref 1] [فَتَفۡشَلُواْ – lest you lose courage]; [وَتَذۡهَبَ رِيحُكُمۡ‌ۖ – and your strength depart]: Meaning: [If you do not obey Allaah and His Messenger, and you start disputing], your resolve will depart. You will lose your strength and the promise you have been given that you will be aided -due to obedience to Allaah and His Messenger- will be withdrawn.

[وَٱصۡبِرُوٓاْ‌ۚ إِنَّ ٱللَّهَ مَعَ ٱلصَّـٰبِرِينَ – and be patient. Surely, Allah is with those who are As-Saabireen (the patient ones, etc.)]: Meaning: Exercise patience in obedience to Allaah [and obedience to His Messenger], for indeed Allaah will aid you and give you victory. Fear your Lord and humble yourselves to Him. [Source: (Tayseer al-kareem Ar-Rahmaan Fee Tafseer Kalaam Al-Mannaan). Abridged & slightly paraphrased]

[Ref 1]: Who causes disunity and disputes in the Ummah? Al-Allaamah Zaid Bin Haadi Al-Madkhali [may Allaah preserve him) said: ‘’The Mubtadi [the innovator] is the cause for the splitting (in the ummah); because splitting is connected to innovation and unity [upon the sound creed and methodology of the Salaf] is connected to the Sunnah. The obligation of refuting the Mukhaalif [the opposer of the truth] is not lifted from the scholar due to anticipation of harm, unless it is harm he is not able to bear. Then [in this case], Allah does not burden a soul beyond what it can bear. The earth is not devoid of people of knowledge who will carry out refutation against the Mubtadi and the Mukhaalif.” [Source: Al Ajwibah Al Mukhtasar Alaa As-ila Al-Ashrati(Page43-44)]

Al-Allaamah Saaleh Al-Fawzaan [may Allaah preserve him] said: The cause of the differences that take place between the callers is the differing in methodologies. And had the callers (may Allaah guide them and grant them success) traversed a singular methodology; and that is the methodology of the Messenger [sallal-laahu-alayhi-wasallam]– that which the Messenger (sallal-laahu-alayhi-sallam) and his companions were upon, then these differences would not have occurred. Therefore, it is obligatory upon all the callers to make their methodology one–upon the Book of Allaah and the Sunnah of the Messenger of Allaah (sallal-laahu-alayhi-wasallam); and that their call is (carried out) for the sake of Allaah and to make the word of Allaah uppermost. Their call should not be for the sake of desires, raising individuals or parties; rather their call should be sincerely for Allaah’s Face, to make Allaah’s word uppermost, to follow the Messenger of Allaah (sallal-laahu-alayhi-wasallam) and to aid his Religion. (So) by way of this the differences will cease.[Source:Al-Ijaabaatul Muhimmah Fil Mashaakil Al-Mulimmah (page:221-222)]

Read the article in this link: The Splitting and Differing in the Ummah is Due to the Innovations and Innovators: 

http://www.salafipublications.com/sps/sp.cfm?subsecID=GSC01&articleID=GSC010003&articlePages=2