Praśna Upaniṣad · 6..1
अथ हैनं सुकेषी भार्गवः पप्रच्छ भगवन् हिरण्यनाभः कौशल्यः शाण्डिल्यशाखायां महाव्रतमुपासीत तं संवत्सरान्तमकामयत मृत्युं मामविन्दतमिति तस्मै स नोपसन्नायाख्यत् तमुवाच प्राणो ब्रह्म तेजो मृत्युं मा गासीति तं ह वा एतद्विद्वानस्मा अकामयत मृत्युं मामविन्दतमिति तमुवाच मा मृत्युं मा गासीत्युक्त्वा तं निर्वेदयामास ता ह वै कलाः प्राणस्य रेवतीर्नाम ऋषयः पितरो देवा लोका भूतानि सर्वाणि यदिदं किञ्च यदिदं किं चित्तद्वै प्राणस्य रेवतीः
atha hainaṃ sukeṣī bhārgavaḥ papraccha bhagavan hiraṇyanābhaḥ kauśalyaḥ śāṇḍilyaśākhāyāṃ mahāvratamupāsīta taṃ saṃvatsarāntamakāmayata mṛtyuṃ māmavindatamiti tasmai sa nopasannāyākhyat tamuvāca prāṇo brahma tejo mṛtyuṃ mā gāsīti taṃ ha vā etadvidvānasamā akāmayata mṛtyuṃ māmavindatamiti tamuvāca mā mṛtyuṃ mā gāsītyuktvā taṃ nirvedayāmāsa tā ha vai kalāḥ prāṇasya revatīrnāma ṛṣayaḥ pitaro devā lokā bhūtāni sarvāṇi yadidaṃ kiñca yadidaṃ kiṃ cittadvai prāṇasya revatīḥ
Then Sukeṣin Bhārgava asked him: Lord, Hiraṇyanābha of Kauśala, of the school of Śāṇḍilya, was practicing the great vow. At the end of the year he desired: “May death not find me”. To him he did not tell who approached; but he told him: “Prāṇa is Brahman, is light; do not say: death”. He, having thus known, at the end of the year desired: “May death not find me”. To him he said: “Do not say death, do not say death”. Having said this, he made him know. These, verily, are the parts of Prāṇa called Revatī: the ṛṣis, the ancestors, the gods, the worlds, all beings, whatever is. Whatever is, verily, are the Revatīs of Prāṇa.
The sixth and final praśna begins. The story of Hiraṇyanābha is told, a practitioner of the mahāvrata (great vow). His desire is to escape death (mṛtyu).
The first teacher did not reveal the secret to one who approached with mere curiosity. But the key teaching is: Prāṇaḥ Brahma — “Prāṇa is Brahman,” and tejaḥ — “is light.”
The instruction “mā mṛtyum mā gāsi” — “do not say death” — is crucial. One who knows Prāṇa as Brahman cannot be touched by death. Death is for one who identifies with the mortal; one who identifies with Prāṇa/Brahman is immortal.
Revatīḥ — “the prosperous, the abundant.” All manifestations — ṛṣis, ancestors, gods, worlds, beings — are “parts” or aspects of Prāṇa. Prāṇa is the basis of all existence.