Śatapatha Brāhmaṇa ("of a hundred paths") 8.7.2.1

8.7.2.1

atha lokampṛṇāmupadadhāti | asau vā ādityo lokampṛṇaiṣa hīmāṃlokānpūrayatyamumevaitadādityamupadadhāti tāṃ sarvāsu citiṣūpadadhātīme vai lokā etāścitayo 'muṃ tadādityameṣu lokeṣu dadhāti tasmādeṣa sarvebhya evaibhyo lokebhyastapati

He then lays down a Lokamprinâ (space-filling brick); the Lokamprinâ, doubtless, is yonder sun, for he fills these worlds: it is thus yonder sun he thereby sets up. He lays down this (Lokamprinâ) in all the (five) layers, for those layers are these (three) worlds: he thus places the sun in (all) these worlds, whence he shines for all these worlds.