What are the reliable sources of religious thought in Islam?

Needless to say religious thought, like other forms of thought, must have reliable sources from which the raw material of its thought originates and upon which it depends. Similarly, the process of reasoning necessary for the solution of mathematical problems must have a series of established mathematical facts and principles.
The single source upon which the divinely revealed religion of Islam depends and upon which it is based, inasmuch as it is based on a revelation of celestial origin is none other than the Holy Quran. It is the Quran which is the definitive treatment of the universal and ever-living prophet hood of the Prophet and it is the content of the Quran that bears the substance of the Islamic call. Of course the facts that the Quran is alone the source of Islamic religious thought dose not eliminate other sources and origins of correct thinking, as will be explained later.