Aqeedah is Tawqeefiyah (which means that) beliefs cannot be established except with a proof from the Sharee’ah (religious texts) there is no room for opinion and speculation.
The sources of Aqeedah are therefore restricted to what is mentioned in the Book and the Sunnah (Ahadeeth of the Prophet) because no one is more knowledgeable than Allah about the obligations due to Him and what He is free from -and after Allah -no one knows more about Allah other than His Messenger
The Manhaj (way) of the Salaf as-Saleh (the pious predecessors) and those who followed them was therefore restricted to the Book and the Sunnah. They believed, affirmed and implemented everything that was established in the Book and the Sunnah concerning the Rights of Allah. They disowned and rejected everything that was not established in either of these two sources
Thus, no differences were found amongst them with regards to beliefs. Their belief was one and their Jama’ah was one because Allah supports whoever holds on to His Book and the Sunnah of His Messenger with a unified position, correct Aqeedah and unity of Manhaj.
“Hold fast, all of you together, to the Rope of Allah (i.e. this Qur’an) and be not divided among yourselves.” [Soorah aal-Imran (3): 103]
and, “Then if there comes to you guidance from Me, then whoever follows My Guidance shall neither go astray nor fall into distress and misery.” [Soorah Taha (20): 123]
They are therefore called ‘the saved sect’ for whom the Messenger testified safety (from the Hell-Fire) when he informed about the splitting of the Ummah (nation) into seventy-three sects -all of them in the Fire except one. When he was asked about this one (saved sect), he replied, “…that which I and my companions are upon this day.” [narrated by Imam Ahmad]
The prophecy of Allah’s Messenger has come to pass. Some people have built their Aqeedah upon other than the Book and the Sunnah such as Ilmul-Kalam -(argumentation based upon) the fundamentals of logic inherited from Greek philosophy. (thus) there occurred deviation from (the correct) Aqeedah, which further resulted in differing of the word, splitting of the Jama’ah and demolition of the united structure of Islam. Imanway.com