大乘起信論義記 2.102

2.102

所言覺義者，謂心體離念。離念相者，等虛空界無所不遍，法界一相即是如來平等法身，依此法身說名本覺。

As for what is called the meaning of enlightenment: it means that the mental substance is free from thoughts. The mark of being free from thoughts is equal to the realm of empty space, pervading everywhere; the single mark of the dharmadhātu is precisely the equal dharmakāya of the Tathāgata. Relying on this dharmakāya, it is spoken of as innate enlightenment.