Chandogya Upanishad 1.18

नैवैतेन सुरभि न दुर्गन्धि विजानात्यपहतपाप्मा ह्येष तेन यदश्नाति यत्पिबति तेनेतरान्प्राणानवति एतमु एवान्ततोऽवित्त्वोत्क्रमति व्याददात्येवान्तत इति ॥ ९ ॥

1.2.9 — naivaitena surabhi na durgandhi vijanatyapahatapapma hyesha tena yadashnati yatpibati tenetaranprananavati etamu evantato'vittvotkramati vyadadatyevantata iti || 9 ||

By it (the breath in the mouth) he distinguishes neither what is good nor what is bad-smelling, for that breath is free from evil. What we eat and drink with it supports the other vital breaths (i. e. the senses, such as smell, &c.) When at the time of death he does not find that breath (in the ​mouth, through which he eats and drinks and lives), then he departs. He opens the mouth at the time of death (as if wishing to eat).

इस मुख्य प्राण से न तो सुगन्ध का, न दुर्गन्ध का भेद-विज्ञान होता है; क्योंकि वह अपहत-पाप्मा (पाप-रहित) है। जो कुछ हम खाते-पीते हैं उसी से वह अन्य प्राणों का पोषण करता है। मृत्यु-काल में जब यह उसे नहीं पाता, तब जीव उत्क्रमण करता है — और मरणासन्न पुरुष तब मुख खोल देता है।