Śatapatha Brāhmaṇa ("of a hundred paths") 6.4.2.10

6.4.2.10

tāḥ ṣaṭ sampadyante | ṣadṛtavaḥ saṃvatsaraḥ saṃvatsaro 'gniryāvānagniryāvatyasya mātrā tāvattadbhavati yadveva saṃvatsaramabhisampadyate tadbṛhatīmabhisampadyate bṛhatī hi saṃvatsaro dvādaśa paurṇamāsyo dvādaśāṣṭakā dvādaśāmāvāsyāstatṣaṭtriṃśatṣaṭtriṃśadakṣarā bṛhatī taṃ dakṣiṇata udañcamāharati dakṣiṇato vā udagyonau retaḥ sicyata eṣo asyaitarhi yoniravicedamāharati retaso 'vicedāya

These (verses) 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. And what comes to be like the year, comes to be like the Brihatî; for the year is the Brihatî,--twelve full moons, twelve eighth days (of the fortnight of waning moon), twelve new moons, that makes thirty-six, and the Brihatî consists of thirty-six syllables. He takes it (the lump of clay) from the right (south) to the left (north) side (of the hole), for from the right side seed is infused into the womb; and this (hole) now is his (Agni's) womb. He takes it thither without stopping, so as not to stop the seed.