瑜伽師地論略纂 8.57

8.57

論「若臥、若默，若住時意業」者，此中，臥應在身業中，以臥時思先明相故，名意業，非臥者是意。

Regarding the treatise's "if lying down, if silent, if mental action at the time of staying": here, lying down should belong to bodily action; because when lying down one contemplates the preceding appearance of light, it is called mental action; it is not that the lying down itself is mental.