菩薩瓔珞本業經 1.36

1.36

「佛子！六為諸佛所護，所謂八解脫觀：聞慧得內假外假二相不可得故，一解脫思慧。內五法外一切法不可得故，二解脫修慧。六觀具足色界五陰空，三解脫、四空、五陰及滅定觀皆不可得故。五解脫如相故。

"Buddha-son! Sixth is to be protected by all buddhas, that is to say, the eight liberative contemplations: through the wisdom arising from listening, one attains the realization that both internal and external provisional marks cannot be apprehended, which is the first liberation of wisdom born of reflection; through the realization that the internal five phenomena and external all phenomena cannot be apprehended, which is the second liberation of wisdom born of cultivation; through the six contemplations fully completing the emptiness of the five aggregates of the form realm, which is the third liberation; and through contemplating the four formless realms, the five aggregates, and the meditative attainment of cessation as all unapprehensible, which is the fifth liberation, because they accord with the mark of suchness.