Surah 67. Al-Mulk, Ayah 10

Reason, properly used, must lead man to a cognition of God's existence and, thus, of the fact that a definite plan underlies all His creation. A logical concomitant of that cognition is the realisation that certain aspects of the divine plan touching upon human life - in particular, the distinction between right and wrong - are being continuously disclosed to man through the medium of the revelation which God bestows on His chosen message-bearers, the prophets. This innate "bond with God" (referred to in 2:27 and explained in the corresponding note [19]) may be broken only at the expense of man's spiritual future, with suffering in the life to come as the inevitable alternative.

Man has himself the power given to him to distinguish good from evil, and he is further helped by the teachings of the great Messengers or World Teachers. Where such Teachers do not come into personal contact with an individual or a generation, the true meaning of their teaching can be understood by means of the Reason which Allah has given to every human soul to judge by. It is failure to follow a man's light sincerely that leads to his degradation and destruction.