首楞嚴義疏注經 10.136

10.136

後際下，釋死後非義。無可道者，言有不有、言無不無，有無二途俱道不得也。現在尚爾，豈況死後不覺不知而言有無耶？故云昏瞢。

From "because the future boundary" downward explains the meaning of "neither after death". "With nothing that can be said": to say it is existent is not existent, to say it is non-existent is not non-existent—neither path of existence or non-existence can be stated. If it is so even in the present, how much more so after death, when without perception and awareness one speaks of existence or non-existence? Hence it is called "dim and muddled".