大般涅槃經義記 8.131

8.131

既言是空，云何名慧？解有四義：一空是慧境故名智慧，故龍樹言「說智智處皆名波若」。

Since it is said to be empty, how is it named wisdom? The explanation has four meanings: first, emptiness is the object of wisdom, hence it is named wisdom; therefore Nāgārjuna says, "Speaking of wisdom and the locus of wisdom, both are called prajñā."