Śatapatha Brāhmaṇa ("of a hundred paths") 6.6.3.16

6.6.3.16

tāstrayodaśa sampadyante | trayodaśa māsāḥ saṃvatsaraḥ saṃvatsaro 'gniryāvānagniryāvatyasya mātrā tāvataivainametadannena prīṇāti

These (kindling-sticks) amount to thirteen;--thirteen months are a year, and Agni is the year: as great as Agni is, as great as is his measure, by so much food he thus gratifies him.