大乘義章 1.56

1.56

問曰：何故虛空之有，有而叵見；佛性之有，有而可見？釋言：虛空說無，故有叵見。佛性之有，說有為有，故有可見。

Question: Why is the existence of empty space existent yet impossible to see, whereas the existence of Buddha-nature is existent and can be seen? Explanation: Empty space is spoken of as non-existent, so its existence is impossible to see. The existence of Buddha-nature is spoken of as existence in terms of being existent; therefore its existence can be seen.