坐禪三昧經 2.9

2.9

漸觀空處，破內外色想，滅有對想，不念種種色想；觀無量空處，常觀色過；念空處定上妙功德。習念是法，逮得空處。

Gradually contemplating the sphere of space, he shatters perceptions of internal and external forms, eradicates perceptions of resistance, and does not think upon perceptions of various forms; contemplating the sphere of boundless space, he constantly contemplates the faults of form; he thinks upon the superior, subtle virtues of the concentration of the sphere of space. Practicing mindfulness of this dharma, he attains the sphere of space.