成唯識論演祕 4.91

4.91

釋曰：異熟識者，即細意識；可了知識，即麁意識。應一身中一時而轉，然不應許，經相違故。如是頌言：無處無容，非前非後，同身同類，二識並生。

The exposition states: The retribution-consciousness is the subtle mental consciousness; the discernible consciousness is the coarse mental consciousness. They would have to operate simultaneously in one body, but this should not be accepted, because it contradicts the sūtras. As the verse states: 'There is no place, no possibility, / Not earlier, not later, / In the same body and of the same category, / For two consciousnesses to arise together.'