Chandogya Upanishad 7.11

tejo vāvādbhyo bhūyaḥ tad vā etad vāyum āgṛhyākāśam abhitapati tadāhur niśocati nitapati varṣiṣyati vā iti teja eva tatpūrvaṃ darśayitvāthāpaḥ sṛjate tad etad ūrdhvābhiś ca tiraścībhiś ca vidyudbhir āhrādāś caranti tasmād āhur vidyotate stanayati varṣiṣyati vā iti teja eva tatpūrvaṃ darśayitvāthāpaḥ sṛjate teja upāssveti

'Fire (tegas) is better than water. For fire united with air, warms the ether. Then people say, It is hot, it burns, it will rain. Thus does fire, after showing this sign (itself) first, create water. And thus again thunderclaps come with lightnings, flashing upwards and across the sky. Then people say, There is lightning and thunder, it will rain. Then also does fire, after showing this sign first, create water. Meditate on fire.

sa yas tejo brahmety upāste tejasvī vai sa tejasvato lokān bhāsvato 'pahatatamaskān abhisidhyati yāvat tejaso gataṃ tatrāsya yathākāmacāro bhavati yas tejo brahmety upāste asti bhagavas tejaso bhūya iti tejaso vāva bhūyo 'stīti tan me bhagavān bravītv iti

'He who meditates on fire as Brahman, obtains, resplendent himself, resplendent worlds, full of light and free of darkness; he is, as it were, lord and master as far as fire reaches—he who meditates on fire as Brahman.' 'Sir, is there something better than fire?' 'Yes, there is something better than fire.' 'Sir, tell it me.'