The Three Fundamental Principles (Thalâthatu ‘l-Usûl) of the Imaam and Mujaddid Muhammad bin ' Abdil-Wahhaab [Died 1206H] -may Allaah have mercy on him- is an important book which every Muslim should read and understand.
The book deals with the three questions asked in the grave: Who is your Lord? What is your dîn? Who is your Prophet?
The book deals with the three questions asked in the grave: Who is your Lord? What is your dîn? Who is your Prophet?

