首楞嚴義疏注經 10.127

10.127

此先將已滅三陰例現存行陰，得四箇非有偏句。又將行存一陰例前已滅三陰，得四箇非無偏句。前後相望，每陰皆得非有非無，成四俱非。現在既爾，死後亦然。現在、未來共成八也，故云死後俱非也。

Here, one first takes the three aggregates that have already ceased as analogous to the currently existing aggregate of formations, obtaining four one-sided propositions of "neither existent". One also takes the one aggregate of formations that currently exists as analogous to the prior three aggregates that have already ceased, obtaining four one-sided propositions of "neither non-existent". Comparing prior and subsequent with each other, for each aggregate one obtains both "neither existent nor non-existent", forming four pairs of "neither". Since it is so in the present, it is likewise after death. The present and the future together make eight; thus it is called "neither [existent nor non-existent] after death".