Shatapatha Brahmana 11.1.1.7

11.1.1.7

yo'sau vaiśākhasyāmāvāsyā tasyāmādadhīta sā rohiṇyā sampadyata ātmā vai prajā paśavo rohiṇyātmanyevaitatprajāyām paśuṣu pratitiṣṭhatyamāvāsyā vā agnyādheyarūpaṃ tasmādamāvāsyāyāmevāgnī ādadhīta paurṇamāsyāmanvārabhetāmāvāsyāyāṃ dīkṣeta

He may lay down the fires on the new moon which falls in the (month) Vaisâkha, for that coincides with the Rohinî (asterism); for the Rohinî means the self, offspring and cattle: he thus becomes established in a self, in offspring and cattle. But, indeed, the new moon is the form of the Agnyâdheya: let him therefore lay down the fires at new moon;--let him perform the preliminary ceremony at full moon, and the initiation ceremony at new moon.