Katha-1-1-7-vaiśvānaraḥ

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

Thus addressed, the father sent him to Death to keep his word and he having gone to the mansion of Death fasted for three nights, Death being away; when Death had gone and returned, his ministers or wife said to inform him, ‘a Brâhman guest, verily like fire itself, enters houses burning them; and good men to allay his burning heat as that of fire, propitiate him by giving water to clean his feet, seat to sit upon, etc. Therefore, Oh Vaivasvata! fetch water to be given to Nachikètas; also because evil consequences are declared in default.

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