瑜伽論記 7.174

7.174

The three portals are: 1. while standing, observing sitting; 2. while sitting, observing reclining; 3. being behind, observing what is before. The present observing [mind] that has already arisen is called "standing"; the future observed [object] about to arise is called "sitting"; the past observed [object] that has already ceased is called "reclining"; the present observing [mind] about to recline is called "sitting"; with what newly arises later, observing the formations that have already arisen and immediately ceased.