Śatapatha Brāhmaṇa ("of a hundred paths") 6.3.2.10

6.3.2.10

tribhiranvicati | trivṛdagniryāvānagniryāvatyasya mātrā tāvataivainametadanvicati tribhiḥ purastādabhimantrayate tatṣaṭ ṣaḍṛtavaḥ saṃvatsaraḥ saṃvatsaro 'gniryāvānagniryāvatyasya mātrā tāvattadbhavati

With three (animals) he searches,--threefold is Agni: as great as Agni is, as great as is his measure, with so much he thus searches for him. By three (formulas) he first addresses (the beasts); that makes six,--six seasons are a year, and the year is Agni: as great as Agni is, as great as is his measure, so great does this become.