瑜伽師地論略纂 8.113

8.113

論云「始從齊處乃至面門，或至鼻端」等者，其息唯至齊處，齊下更無出處，還復乃至從口出及鼻端出也。

Where the treatise says, "beginning from the region of the navel, up to the mouth, or reaching the tip of the nose," and so forth: the breath reaches only down to the region of the navel; below the navel there is no other exit, and returning back, it exits from the mouth and the tip of the nose.