大乘起信論裂網疏 5.10

5.10

為除彼執，明虛空相唯是分別，實不可得。有見、有對、待於諸色，以心分別說名虛空。色既唯是妄心分別，當知虛空亦無有體。

To remove that attachment, it is explained that the mark of empty space is merely a discrimination and cannot truly be found. Because it is visible and has resistance, and is relative to physical forms, it is discriminated by the mind and called empty space. Since physical form is merely a discrimination of the deluded mind, one should know that empty space also has no substantial entity.