大乘起信論裂網疏 4.100

4.100

此先觀色蘊不成就也。微塵設有方分便可分析，決非實有；若無方分便是非色。故知粗細諸色皆是妄心所現相分，心外實無色也。

This first contemplates that the aggregate of physical form is unestablished. If a subtle atom has directional parts, then it can be analyzed and is definitively not real; if it has no directional parts, then it is not physical form. Therefore, one knows that all gross and subtle physical forms are mere objective aspects manifested by the deluded mind; outside of the mind there is truly no physical form.