成唯識論述記 4.423

4.423

述曰：第二申難中。設令乃至頞部曇位，眼等轉識攝在四蘊名中。若無此本識者，六識不俱故，說誰為識。

The Commentary states: In the second part, formulating the objection: Even up to the stage of the arbuda, the evolving consciousnesses such as the visual consciousness are subsumed under the name of the four aggregates. If this fundamental consciousness did not exist, then because the six consciousnesses do not operate concurrently, what could be called consciousness?