大乘起信論義記 3.239

3.239

別中本來色心不二者，謂彼所現報化之色不異法身真心，如波與水本來無二。言以色性即智等者，明色即心顯前不二。以色即心故，遂令色相都盡，故就其本但云智身，智謂本覺心智也。言以智性即色故說法身遍一切處者，明心即色顯前不二，如水遍在波中故也。

In the specific explanation, 'from the beginning form and mind have been non-dual' means that the forms of the reward and transformation [bodies] manifested therein are not different from the true mind of the dharmakāya, just as waves and water have originally been non-dual. The statement from 'because the nature of form is precisely cognition' and so forth clarifies that form is precisely mind, revealing the preceding non-duality. Because form is precisely mind, it immediately causes marks of form to be completely exhausted; therefore, in terms of its origin, it merely speaks of the 'cognition-body.' 'Cognition' refers to the mind-cognition of innate enlightenment. The statement 'because the nature of cognition is precisely form, the dharmakāya is said to pervade all places' clarifies that mind is precisely form, revealing the preceding non-duality, just as water is everywhere within the waves.