Chandogya Upanishad 4.7.1

4.7.1

haṃsas te pādaṃ vakteti \
sa ha śvo bhūte gā abhiprasthāpayāṃ cakāra \
tā yatra abhisāyaṃ babhūvus tatra agnim upasamādhāya gā uparudhya samidham ādhāya paścād agneḥ prāṅ upopaviveśa \\407.1\

1. A swan will tell you a quarter.’ He then, when it was the morrow, drove the cows on. Where they came at evening, there he built a fire, penned in the cows, laid on the fuel, and sat down to the west of the fire, facing the east.