Śatapatha Brāhmaṇa ("of a hundred paths") 9.3.3.9

9.3.3.9

trayodaśaitāni nāmāni bhavanti | trayodaśa māsāḥ saṃvatsarastrayodaśāgneścitipurīṣāṇi yāvānagniryāvatyasya mātrā tāvataivainametatprīṇāti yadveva nāmagrāhaṃ juhoti nāmagrāhamevainametadabhiṣiñcati

There are thirteen of these names,--a year consists of thirteen months, and the layers and fillings of the fire-altar amount to thirteen: as great as Agni is, as great as is his measure, with so much he thus gratifies him. And as to why he offers while mentioning names,--it is thus in mentioning his (Agni's) names that he consecrates him.