大方廣圓覺修多羅了義經略疏 2.103

2.103

This is fundamental avidyā. Because failing to penetrate the nature and characteristics of the dharmadhātu obstructs right knowledge and vision. Thus that treatise says: 'This mind from the beginning is inherently pure in its self-nature, but because of not penetrating the one dharmadhātu, the mind does not correspond, and suddenly thoughts arise, which is called avidyā.'