成唯識論述記 4.409

4.409

述曰：又第六識境不定故，緣境轉易。此命終時行相微細，緣一類境，非第六識有是相狀。

The Commentary states: Furthermore, because the object of the sixth consciousness is unfixed, its conditioning of objects shifts and changes. At this time of death, the active mode is subtle and conditions a uniform object; the sixth consciousness does not possess such characteristics.