Śatapatha Brāhmaṇa ("of a hundred paths") 10.5.2.14

10.5.2.14

sa eṣa evendraḥ yo'yaṃ dakṣiṇe'kṣanpuruṣo'theyamindrāṇī tābhyāṃ devā etāṃ vidhṛtimakurvannāsikāṃ tasmājjāyāyā ante nāśnīyādvīryavānhāsmājjāyate vīryavantamu ha sā janayati yasyā ante nāśnāti

And, indeed, he is the breath (prâna), for it is he (the man in the eye) that leads forward (pranayati) all these creatures. These vital airs (prâna) are his own (sva); and when he sleeps (svapiti) then these vital airs take possession of him as his own (svâ api-yanti): hence (the term) 'svâpyaya (being taken possession of by one's own people),' 'svâpyaya' doubtless being what they mystically call 'svapna (sleep),' for the gods love the mystic.