Śatapatha Brāhmaṇa ("of a hundred paths") 4.1.2.26

4.1.2.26

tāni vā aniṅgyamānāni śere | ā tṛtīyasavanāttāyate yajña eti vai tadyattāyate tasmādimāni vayāṃsi vigṛhya pakṣāvanāyuvānāni patanti tāni punastṛtīyasavane prayujyante tasmādimāni vayāṃsi samāsam pakṣāvāyuvānāni patanti yajñasyaivaitadvidhāmanu

They repose without being moved until the evening Soma feast. The sacrifice is spread along; but what is spread along moves, whence those birds fly spreading their wings, not drawing them in. At the evening Soma feast they are again used; whence these birds fly drawing in their wings to fold them: this indeed is after the manner of the sacrifice.