瑜伽論記 15.409

15.409

二、辨涅槃虛空名界所以，由證涅槃眾苦皆滅，故云持苦不生。是故涅槃立在法界，虛空無礙，持身往來，運動作用。又空為勝緣，持眼見用，故云持身眼等運動用義。

Second, differentiating why nirvāṇa and space are called 'elements': because through realizing nirvāṇa all suffering is extinguished, it is therefore said to sustain suffering so that it does not arise. For this reason, nirvāṇa is established within the factor-element (dharmadhātu). Space is unobstructed, sustaining the body's coming and going, movement and action. Furthermore, space serves as a supreme condition, sustaining the eye's function of seeing; hence it is said to have the meaning of sustaining the movements and functions of the body, eye, and so forth.