大乘起信論別記 1.115

1.115

言「猶如明鏡現色相」者，如四卷經云「大惠！廣說有三種識，廣說八相。何等為三？謂真識、現識、分別事識。譬如明鏡，持諸色像；現識處現，亦復如是。」又此文中，說現義云「以一切時任運而起常在前故」。當知現識定在第八，其業識等與此作本其相彌細，如何強將置七識中，甚可乎？

As for "just like a bright mirror manifesting visual forms": as the Four-fascicle Laṅkāvatārasūtra says: "Mahāmati! Broadly speaking, there are three kinds of consciousness and eight characteristics. What are the three? They are the true consciousness, the manifesting consciousness, and the consciousness that discriminates objects. Just as a bright mirror holds all forms and images, so too does the manifesting consciousness manifest [them]." Furthermore, in this text, explaining the meaning of manifestation, it says: "Because at all times it arises spontaneously and is always present before [the mind]." One should know that the manifesting consciousness definitely belongs to the eighth [consciousness]. The karmic consciousness and so forth serve as the root for this, and their characteristics are even more subtle; how could one forcibly place them among the seven consciousnesses? How could that be acceptable?