大乘起信論裂網疏 4.66

4.66

This first reveals the essence of the Mahāyāna. "All ordinary beings" refers to the six ordinary dharmadhātus, which, together with the śrāvakas and the others, constitute the ten dharmadhātus. Each ordinary being up to each Buddha fully possesses the complete essence of tathatā, and there are not two tathatās: in delusion it does not decrease, and in awakening it does not increase; the prior limit is without beginning and the posterior limit is without end; hence it is said to be "constant, eternal, and ultimate."