成唯識論述記 2.879

2.879

述曰：第三、釋頌顯前徵，總釋頌言成因緣理。此由未顯，何以得知互為因緣，是此經意。

The Commentary states: Third, explaining the verse to clarify the preceding query, giving a general explanation of the words of the verse to establish the principle of cause and condition (hetu-pratyaya). Since this has not yet been clarified, [one asks] how we know that mutual cause and condition is the meaning of this sūtra.