仁王護國般若波羅蜜多經疏 2.574

2.574

解曰：以一切法者，所謂二諦、生死涅槃、境智俱空。空空故空者，能所俱空、我法俱空，故云空空。照解空寂，故云空也。從此第二徵之所以。

Exposition: Regarding 'Because all phenomena': the so-called two truths, saṃsāra and nirvāṇa, and object and cognition are all empty. Regarding 'empty of emptiness, they are empty': subject and object are both empty, self and phenomena are both empty; hence it says 'empty of emptiness'. Illumination and understanding are empty and quiescent; hence it says 'empty'. From here, the second part inquires into the reason.