大般涅槃經義記 6.423

6.423

第三對中，初句就其未聞之時難破有聞，明其唯是不聞不聞，非不聞聞。後句就其不聞之時難破不聞，彰先有聞，先有聞，　後得聖時聞於可聞，非聞不聞。前中，「世尊若不聞聞者」審定如來未聞之時已有聞性，名不聞聞。

In the third pair, the first phrase refutes the existence of hearing with respect to the time when it has not yet been heard, clarifying that it is solely not hearing and not hearing, not hearing what is not heard. The latter phrase refutes not hearing with respect to the time of not hearing, showing that previously there was hearing: if previously there was hearing, then afterwards when attaining sagehood one hears what can be heard, not hearing what is not heard. In the former part, "World-Honored One, if what is not heard is heard" investigates and determines that at the time when the Tathāgata had not yet heard, he already had the nature of hearing, which is called hearing what is not heard.