Katha-2-2-5-na prāṇena

Sri Shankara’s Commentary (Bhashya) translated by S. Sitarama Sastri

The theory may be urged ‘that the body becomes destroyed only by the exit of prana, apâna, etc., and not by the exit of the âtman distinct from these; for, man lives only by prana and the rest’. This is not so; not by prâna, not by apâna, not by the eyes, etc., does a mortal having a body live. These acting jointly for the benefit of some other cannot be the source of life. The existence of houses, etc., composite in their nature, has not been seen in the world to be undirected by some other not connected with them, for whose benefit they exist; so also, it should be in the case of the combination of prâna and the rest. Therefore, it is by some other alone, dissimilar to the combination of prâpa and the rest, all these combined maintain their life. On which âtman, dissimilar to those combined, the really existent and the highest, these two prâna, and apâna combined with the eyes and the rest, depend and for the benefit of whom (not so combined) prâna, apâna and the rest perform their functions in combination, he is established to be other than they.

Links
Various resources on the Kathopanishad
Upanishad Series – Katopanishad Commentary by Swami Chinmayananda