成唯識論述記 2.507

2.507

述曰：有、無並難，色中有空，色體與空體應相雜。量云：色中虛空體應即色；處無別故；如此處色體。相雜者，是一義，若此色體中無有虛空，虛空應不遍一切法；不遍一切法故，應是有為；如地、水別。

The Commentary states: Both [the alternatives of] existence and non-existence are refuted. If there is space within form, the substance of form and the substance of space would necessarily be intermixed. A syllogism states: The substance of space within form must be identical to form; because their location is not distinct; just like the substance of form at this location. 'Intermixed' means they are identical. If there is no space within this substance of form, space would not pervade all phenomena; and because it would not pervade all phenomena, it would be conditioned; just as earth and water are distinct.