首楞嚴義疏注經 4.609

4.609

睡人六識歸種，思覺不行，但任運聞，即真聞性。若唯約喻，睡人應無聞性，但約不隨根起，非由作意，故是真聞。如下文云「縱令在夢想，不為不思無，覺觀出思惟，身心不能及。」故知即顯真聞，不須約喻。

When a person sleeps, the six consciousnesses return to their seeds, and conceptual thought does not operate; yet they naturally hear, which is the true nature of hearing itself. If viewed merely as an analogy, a sleeping person should have no nature of hearing; but because it does not arise following the faculties and does not proceed from intention, it is true hearing. As the text below says: "Even when in dream-thoughts, / It is not absent because of not thinking; / Awakening and observing transcend conceptual thought, / Beyond the reach of body and mind." Hence we know this directly reveals true hearing, without requiring it to be merely an analogy.