成唯識論述記 3.696

3.696

述曰：第二外人問曰：何知此識三乘皆捨，阿羅漢號通在三乘？故論總問：「云何知然」。

The Commentary states: Second, the outsider asks: "How is it known that this consciousness is abandoned by all three vehicles, and that the title of arhat applies generally to the three vehicles?" Therefore, the treatise raises the general question: "How is this known to be so?"