大乘起信論義記 3.238

3.238

'Answer: Because this very dharmakāya is the substance of form, it can manifest form. That is to say, from the beginning, form and mind have been non-dual. Because the nature of form is precisely cognition, the substance of form has no shape, and is named the cognition-body (jñānakāya); because the nature of cognition is precisely form, the dharmakāya is said to pervade all places.'