Shatapatha Brahmana 6.2.3.5

6.2.3.5

te 'bruvan | cetayadhvameveti citimicateti vāva tadabruvannita ūrdhvamicateti teṣāṃ cetayamānānām parameṣṭhī divaṃ tṛtīyaṃ svayamātṛṇāṃ citimapaśyattasmāttām parameṣṭhinopadadhāti

They said, 'Meditate ye yet!'--whereby no doubt they said, 'Seek ye a layer! seek ye (to build) from hence upwards!' Whilst they were meditating, Parameshthin saw the sky, as a third naturally-perforated layer: whence it is by Parameshthin (the most high) he lays on that (brick).