唯識二十論述記 1.97

1.97

述曰：即第三難，頌第三句，「相續不定」，不應成難。言「相續」者，有情異名，前蘊始盡，後蘊即生，故言「相續」。或非常、一，簡異外宗，亦言相續。謂既無外境許有此識生，如同一山處，及同一時間，有多相續，皆共緣見，何不決定隨一相續，緣山識生，所餘有情，此識不起。

The Commentary says: This is the third objection, corresponding to the third line of the verse: the objection that 'non-determination of streams' should not be established. The term 'stream' is an alternative name for a sentient being: as the preceding aggregates end, the succeeding aggregates immediately arise, hence it is called a 'stream.' Alternatively, because it is not permanent or unitary, distinguishing it from non-Buddhist tenets, it is also called a stream. That is, since there is no external object, yet you grant that this consciousness arises, just as in the place of a single mountain and at a single time there are multiple streams who all collectively perceive it, why does consciousness cognizing the mountain not arise determinately in just any one stream, while in the remaining sentient beings this consciousness does not arise?