The scholars of the early and later times agreed by consensus (ijmaa') that the fundamentals which are accepted and counted for establishment of rulings, and for clarification of what is permissible and what is forbidden are: Firstly, that which occurs in the Mighty Book of Allaah, which is not approached by falsehood from any direction. And also the Sunnah of Allaah's Messenger, Muhammad (may the peace and blessings of Allaah be upon him), the one who did not speak from his desires, rather he spoke with Revelation inspired. And then the consensus (ijmaa') of the scholars of the Muslims. Thereafter the scholars differ with regard to other fundamentals, the most important of which is 'al-Qiyaas' (analogy), and the majority of the people of knowledge hold that it is a proof as long as its accepted conditions are present. Then the proofs for these principles are more than can be counted and are well-known. The treatise in front of you discusses in particular the second fundamental regarding the obligation of adhering to the Sunnah of the Messenger (salallaahu alayhi wassallam), its importance as mentioned in the Quraan, the Prophetic narrations and the statements of the early Scholars and the fact that its rejection is unbelief.