成唯識論述記 5.722

5.722

述曰：此第二解，依不共根、不共境故，說有六種，非謂盡理，而識類別實有八種。大乘之中，於處門中不開識者，以此理通。第八卷中，當廣證理。

The Commentary states: This is the second explanation: because they rely on unshared faculties and unshared objects, six kinds are spoken of, which does not exhaust the principle; in reality, classified by kind of consciousness, there are eight. That consciousness is not expanded [into eight] under the classification of sense bases (āyatana) in the Mahāyāna is justified by this principle. In the eighth fascicle, this reasoning will be broadly demonstrated.