Śatapatha Brāhmaṇa ("of a hundred paths") 8.5.3.4

8.5.3.4

yadveva stomabhāgā upadadhāti | etadvai devā virājaṃ citiṃ citvā samārohaṃste 'bruvaṃścetayadhvamiti citimicateti vāva tadabruvaṃste cetayamānā nākameva svargaṃ lokamapaśyaṃstamupādadhata sa yaḥ sa nākaḥ svargo loka etāstā stomabhāgāstadyadetā upadadhāti nākamevaitatsvargaṃ lokamupadhatte

And as to why he lays down the Stomabhâgâs. Now the gods, having laid down the far-shining layer, mounted it. They spake, 'Meditate ye!' whereby, doubtless, they meant to say, 'Seek ye a layer!' Whilst meditating, they saw even the firmament, the heavenly world, and laid it down. Now that same firmament, the heavenly world, indeed is the same as these Stomabhâgâs, and thus in laying down these, he lays down the firmament, the heavenly world.