Quotes from Compendium of Abhidharma, Vol. 3

(Abhidharma-samuccaya)

Bodhisattva Asaṅga 

“What is the characteristic of emptiness (śūnyatā)?
It is the non-existence (abhāva) of a certain thing, there. To observe (samanupaśyanā) in this way is emptiness.
Again, it is the existence (bhāva) of another thing, there.
In this way there is real knowledge (yathābhūtajñāna). This is called emptiness perceived by penetration (avatāra). Real knowledge means informed meaning.

What is the meaning of the non-existence of a certain thing, there? It is the non-existence in the aggregates, elements and spheres, of a self or anything pertaining to a self of a permanent, enduring, eternal and immovable nature. This is their emptiness.

What is the meaning of the existence of another thing, there? It is the fact that there is non-self in them. It is the non-existence of self, and the existence of non-self. It is with this meaning that the Blessed One said: ‘Existence is real knowledge of an existing thing; non-existence is real knowledge of a non-existing thing.’"

《大乘阿毘達磨集論》卷三

無著菩薩

何等空相？謂若於是處此非有，由此理正觀為空；若於是處餘是有，由此理如實知有，是名善入空性。如實知者，不顛倒義。
於何處誰非有？於蘊、界、處，常恒凝住不變壞法，我、我所等非有。由此理，彼皆是空。
於何處誰餘有？即此處無我性。此我無性，無我有性，是謂空性。故薄伽梵密意說言：有如實知有，無如實知無。