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

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.