成唯識論述記 2.571

2.571

述曰：為外道等心、心所外執實有境故，假說唯有識，非「唯識」言便有實識。

The Commentary states: Because non-Buddhists and others grasp at really existent objects outside of mind and mental factors, it is provisionally said that there is consciousness-only; it is not that the word "consciousness-only" implies that there is a real consciousness.