佛頂尊勝陀羅尼經教跡義記 2.51

2.51

唐云如虛空清淨也。解曰：詳觀此意，法諭雙彰，二因滌除淨若空界，賢聖分位修證不同，唯有佛身如虛空淨。又解：一切諸法體性空寂，諸佛妙智依空而轉，所有建立及不建立，空與不空智相常住猶如虛空，然此虛空體虛非實，唯有妙智功用不窮，故假諭云虛空清淨也。

In Chinese it means: "Pure like space." The explanation states: If one carefully considers this meaning, both doctrine and metaphor are made manifest: the two causes are washed away, pure like the realm of space; the stages of the worthy and the noble differ in practice and realization, and only the Buddha's body is pure like space. Another explanation: The essential nature of all phenomena is empty and quiescent, and the wondrous wisdom of the Buddhas turns in dependence upon emptiness; all that is established and not established, empty and not empty, the marks of wisdom are eternally abiding just like space; however, the essence of this space is empty and not real, whereas only the wondrous wisdom has inexhaustible function; thus it is metaphorically spoken of as "pure like space."