成唯識論述記 2.281

2.281

述曰：下有三難，初內外相同難，此牒外救。若無別實眾同分者，即緣界、趣及四生等，同言、同智應不得生，以無能同相似法故；無不生心，要緣有故。

The Commentary states: Below there are three objections; the first is the objection regarding the similarity between internal and external, which cites the outsider's defense. If there is no separate and real nikāya-sabhāga, then common expression and common cognition directed toward realms, destinies, the four modes of birth, and so forth, should not be able to arise, because there would be no similar dharma capable of making them alike; for a mind does not arise without an object—it must condition an existent.