Śatapatha Brāhmaṇa ("of a hundred paths") 8.2.1.2

8.2.1.2

te 'bruvan | cetayadhvamiti citimicateti vāva tadabruvannita ūrdhvamicateti te cetayamānā etāṃ dvitīyāṃ citimapaśyanyadūrdhvam pṛthivyā arvācīnamantarikṣātteṣāmeṣa loko 'dhruva ivāpratiṣṭhita iva manasyāsīt

They spake, 'Meditate ye!'--whereby, doubtless, they meant to say, 'Seek ye a layer! Seek ye (to build) from hence upwards!' Whilst meditating, they saw this second layer: what there is above the earth, and on this side of the atmosphere, that world was to their mind, as it were, unfirm and unsettled.