Shatapatha Brahmana 10.4.2.1

10.4.2.1

saṃvatsaro vai prajāpatiragniḥ somo rājā candramāḥ sa ha svayamevātmānam proce yajñavacase rājastambāyanāya yāvanti vāva me jyotīṃṣi tāvatyo ma iṣṭakā iti

Verily, Pragâpati, the year, is Agni, and King Soma, the moon. He himself, indeed, proclaimed (taught) his own self to Yagñavakas Râgastambâyana, saying, 'As many lights as there are of mine, so many are my bricks.'