大乘起信論裂網疏 4.66

4.66

此先示大乘體也。一切凡夫，即六凡法界，并聲聞等，則成十法界也。一一凡夫乃至一一諸佛無不各具真如全體，而亦無二真如在迷不減、在悟不增，前際無始、後際無終，故云常恒究竟也。

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."