大毘盧遮那成佛經疏 13.47

13.47

夫虛空雖無相無礙，而不能成辦大事。今此如來之空雖無所依，而能成就一切勝上之事，過彼虛空不可為匹也。大悲體者，即是如來之眼。此眼從大悲生，能生大悲也（更問）。

Now, although empty space has no characteristics and is unobstructed, it cannot accomplish great affairs. Now, although this emptiness of the Tathāgata has nothing to rely upon, it can accomplish all supreme affairs; surpassing that empty space, it cannot be rivaled. The essence of great compassion is the Tathāgata's eye. This eye is born from great compassion and can generate great compassion (inquire further into this).