瑜伽論記 7.174

7.174

三門者，一、住觀於坐；二、坐觀於臥；三、在後觀前。現在能觀已起名住，未來所觀將起名坐，過去所觀已滅名臥現在能觀將臥名坐，以後新起觀無間滅已起諸行。

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.