Śatapatha Brāhmaṇa ("of a hundred paths") 4.1.2.25

4.1.2.25

tāni vā aniṅgyamānāni śere | ā tṛtīyasavanāttasmādime manuṣyāḥ svapanti tāni punastṛtīyasavane prajujyante tasmādime manuṣyāḥ suptvā prabudhyante te 'niśitāścarācarā yajñasyaivaitadvidhāmanu vaya iva ha vai yajño vidhīyate tasyopāṃśvantaryāmāveva pakṣāvātmopāṃśusavanaḥ

Now these (cups and stone) repose without being moved until the evening Soma feast, whence men sleep here on earth; and at the evening Soma feast they are used again, whence these men, having slept, awake and are bustling and restless;--this, forsooth, is after the manner of the sacrifice, for the sacrifice is fashioned like a bird: the Upâmsu and Antaryâma (grahas) are its wings, and the Upâmsusavana (stone) its body.