Dividing the religion into basic matters (usool) and minor issues (furoo’)
Question

                Is it correct to regard the basic matters (usool) of religion as purely theoretical, and the minor issues (furoo’) as purely practical?
Praise be to Allah.The basic matters (usool) of 
          religion are not purely theoretical, and there is no separation between 
          belief and practice in Islam. There is nothing in the Qur’aan or the 
          Sunnah of the Messenger of Allaah  
          (peace and blessings of Allaah be upon him) to suggest that the basic 
          matters have to do only with beliefs and that the minor issues have 
          to do only with practice. This separation originated with the Mu’tazilah, 
          who are the ones who separated the basic matters and minor principles 
          in this manner.