Patanjali Yoga sutra 2,5.

 Ignorance is taking that which is non-eternal, impure,

painful, and non-Self, for the eternal, pure, happy, Atman (Self). All these various sorts of impression have one source:ignorance. We have first to learn what ignorance is.All of us think that “I am the body,”and not the Self, the pure,the effulgent, the ever blissful,and that is ignorance. We think of man,and see man as body.This is the great delusion.