華嚴經內章門等雜孔目章 1.42

1.42

五云何業用不可得耶？謂若無諸識同時生起業用俱轉，不應道理。所以者何？略說識業有四種，謂了別外器、了別依止、能了別我、了別境界。如是四種識了別業，一一剎那俱現，可得非於一識一剎那中有如是等差別業用，是故必有諸識俱起。

Fifth, how is it that "operations are unobtainable"? If there were no simultaneous arising of the various consciousnesses, their operations occurring concurrently would be unreasonable. Why is this? Briefly stated, the operations of consciousness are of four kinds: discerning the external vessel [world], discerning the support [of the body], discerning the self, and discerning objects. Such four kinds of discerning operations of consciousness can be found to appear concurrently at every single moment; it is not the case that such distinct operations could exist within a single consciousness in a single moment. Therefore, there must be the simultaneous arising of various consciousnesses.