Śatapatha Brāhmaṇa ("of a hundred paths") 11.2.4.1

11.2.4.1

eṣa vai pūrṇamāḥ ya eṣa tapatyaharaharhyevaiṣa pūrṇo'thaiṣa eva darśo yaccandramā dṛdṛśa iva hyeṣaḥ

The full moon, doubtless, is the same as that burning (sun), for he, indeed, is full day by day; and the new moon (darsa) is the same as the moon, for he appears (dars), as it were.