Śatapatha Brāhmaṇa ("of a hundred paths") 6.5.4.9

6.5.4.9

sa vai khanatyekena | avadadhātyekenābhīnddha ekena śrapayatyekena dvābhyām pacati tasmāddviḥ saṃvatsarasyānnam pacyate tāni ṣaṭ sampadyante ṣadṛtavaḥ saṃvatsaraḥ saṃvatsaro 'gniryāvānagniryāvatyasya mātrā tāvattadbhavati

Now he digs with one (formula), he sets down (the fire-pan) with one, he kindles with one, he heats with one, he bakes (pak) with two, whence twice in the year food is ripened (pak); these amount to six,--six seasons are a year, and Agni is the year: as great as Agni is, as great as is his measure, so great does this become.