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

Shaikh Saaleh Al-Fawzaan (may Allaah preserve him) stated:

The cause of the differing 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-making Allaah’s word uppermost; following the Messenger of Allaah (sallal-laahu-alayhi-wasallam) and to aid His Religion.  (So) by way of this the differing will cease. [Source: Al-Ijaabaatul Muhimmah Fil Mashaakil Al-Mulimmah (page:221-222)]

Shaikh Zaid Ibn Hadee al Madkhalee (rahimahullaah) said:

The Mubtadi (innovator) is the cause for the splitting (in the Ummah). That is 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)]