唯識二十論述記 1.51

1.51

答：據梵本說亦無「一」字，但言唯心。今義釋言：唯獨但義，一無二義，名異義同。謂無外境，唯有心故，名為一心，非說心體但是一物。

Answer: According to the Sanskrit text, there is also no word "one"; it merely says "only mind" (citta-mātra). Now, interpreting the meaning: "only" (mātra) has the sense of sole or exclusive; "one" has the sense of having no second; their names differ but their meaning is the same. That is, because there are no external objects and there is only mind, it is termed "one mind," not that the substance of mind is merely a single entity.