唯識二十論述記 1.39

1.39

問：曰欲、色界有色，遮此說唯心，無色界色無，應不言唯識。此難不然。所執實皆無，遮此名唯識，非但遮色有，故說三界唯心，亦無所執唯識，及餘虛空法等一切境故。又經部師說：無色界諸心、心所，是無色相，無體，無實所取境義，顯現所依，恐彼執為非心、心所，故說三界皆唯有心。

Question: The desire and form realms have form; to exclude this it states mind-only. In the formless realm form does not exist, so it should not say vijñapti-mātra. [Answer:] This objection is incorrect. What is grasped is entirely non-existent; to exclude this is called vijñapti-mātra, not merely to exclude the existence of form; therefore it says the three realms are mind-only, because all objects such as imagined vijñapti-mātra and other empty space phenomena are also absent. Furthermore, the Sautrāntikas state: the minds and mental factors in the formless realm lack form-aspects, lack substantial entity, lack real grasped object-meanings, and are the basis of manifestation; fearing that they would grasp them as non-minds and non-mental factors, it states that the three realms are all mind-only.