瑜伽師地論略纂 6.59

6.59

「不淨生處超越因故」者，三惡趣、八無暇，名不淨生處。身語意三淨業，名超彼因。

"Because of being the cause for transcending impure birthplaces": the three miserable destinies and the eight conditions of no opportunity are called impure birthplaces. The three pure karmas of body, speech, and mind are called the causes for transcending them.