大般涅槃經義記 6.22

6.22

「所以」下釋，先問、後斷。以性常住故非內、非外，良以內空隨法治空，佛性是常，與彼全別，所以不在。

From 'For what reason' below is the explanation, first asking and then determining. Because its nature is permanently abiding, it is neither internal nor external; indeed, because internal emptiness is an emptiness that remedies in accordance with dharmas, while buddha-nature is permanent and entirely distinct from it, it is therefore not present.