Chandogya Upanishad 7.12

ākāśo vāva tejaso bhūyān ākāśe vai sūryācandramasāv ubhau vidyun nakṣatrāṇy agniḥ ākāśenāhvāyati ākāśena śṛṇoti ākāśena pratiśṛṇoti ākāśe ramate ākāśe na ramate ākāśe jāyate ākāśam abhijāyate ākāśam upāssveti

'Ether (or space) is better than fire. For in the ether exist both sun and moon, the lightning, stars, and fire (agni). Through the ether we call, through the ether we hear, through the ether we answer. In the ether or space we rejoice (when we are together), and rejoice not (when we are separated). In the ether everything is born, and towards the ether everything tends when it is born. Meditate on ether.

sa ya ākāśaṃ brahmety upāste ākāśavato vai sa lokān prakāśavato 'saṃbādhān urugāyavato 'bhisidhyati yāvad ākāśasya gataṃ tatrāsya yathākāmacāro bhavati ya ākāśaṃ brahmety upāste asti bhagava ākāśād bhūya iti ākāśād vāva bhūyo 'stīti tan me bhagavān bravītv iti

He who meditates on ether as Brahman, obtains the worlds of ether and of light, which are free from pressure and pain, wide and spacious; he is, as it were, lord and master as far as ether reaches — he who meditates on ether as Brahman.' 'Sir, is there something better than ether?' 'Yes, there is something better than ether.' 'Sir, tell it me.'