Ibn Majah

1؎: That is, among the Children of Israel, all corruption arose from the spread of personal opinion and turning away from revelation, and the destruction of every community occurs in the same way: when they give precedence to their own opinions over divine revelation, they are ruined. In this Ummah as well, ever since people began to turn away from the Book and the Sunnah, and started issuing legal verdicts (fatwas) based on false opinions and corrupt analogies (qiyas), and the later generations gave preference to these opinions and analogies over divine revelation and the guidance of the Messenger, from that very moment a state of division and discord emerged, and various sects came into existence, and unity and harmony within the Ummah began to diminish. Each group, turning away from the Book and the Sunnah, appointed one individual as their leader and guide, and made him the standard for the Book and the Sunnah, whereas the fundamental principle is that in all matters, the reference and source should be the Book and the Sunnah and the understanding and methodology of the righteous predecessors (salaf salihin), and turning towards this is the guarantee of the Ummah’s unity. This is because the Noble Prophet (sallallahu alayhi wa sallam) said: “«تركت فيكم أمرين لن تضلّوا ما إن تمسكتم بهما كتاب الله وسنتي»” I am leaving among you two things, the Book and the Sunnah; as long as you hold fast to them (in practice), you will never go astray.”