大乘起信論廣釋卷第三．四．五 4.67

4.67

[Treatise:] In all ordinary beings, [śrāvakas, pratyekabuddhas, bodhisattvas, and buddhas, it neither increases nor decreases; it is not born in the prior limit and does not cease in the posterior limit;] it is ultimately eternal and constant.
[Commentary:] Next is the separate explanation of the meaning of the two greatnesses. Within this, the two greatnesses are divided into two. This is the first, the greatness of substance. Although persons are graded as superior or inferior according to their stages, the substance, following the person, has never increased or decreased. "It is not born in the prior limit," and so forth, explains the reason for neither increasing nor decreasing: because it is not born in the prior limit, there is no increase; because it does not cease in the posterior limit, there is no cessation. That is, the ordinary stage is the prior limit, and the buddha stage is the posterior limit. "Ultimately eternal and constant" explains the meaning of neither arising nor ceasing: because it is eternal, it is not born in the prior limit; because it is constant, it does not cease in the posterior limit. Since it is eternal and constant, from ordinary beings to buddhas, its substance is ultimately without alteration.