Chandogya Upanishad 4.13

atha hainam āhavanīyo 'nuśaśāsa prāṇa ākāśo dyaur vidyud iti ya eṣa vidyuti puruṣo dṛśyate so 'ham asmi sa evāham asmīti

Then the Âhavanîya fire taught him: 'Breath, ether, heaven, and lightning (these are my forms). The person that is seen in the lightning, I am he, I am he indeed.

sa ya etam evaṃ vidvān upāste apahate pāpakṛtyām lokī bhavati sarvam āyur eti jyog jīvati nāsyāvarapuruṣāḥ kṣīyante upa vayaṃ taṃ bhuñjāmo 'smiṃś ca loke 'muṣmiṃś ca ya etam evaṃ vidvān upāste

'He who knowing this meditates on him, destroys sin, obtains the world (of Agni Âhavanîya), reaches his full age, and lives long; his descendants do not perish. We guard him in this world and in the other, whosoever knowing this meditates on him.'