Śatapatha Brāhmaṇa ("of a hundred paths") 6.2.2.34

6.2.2.34

atha yāni daśa | sā daśākṣarā virāḍvirāḍagnirdaśa diśo diśo 'gnirdaśa prāṇāḥ prāṇā agniryāvānagniryāvatyasya mātrā tāvattadbhavati

And what (remaining) ten there are (in those fifty-eight), they are the Virâg, consisting of ten syllables; and the Virâg is Agni,--there are ten regions, and the regions are Agni; ten vital airs, and the vital airs are Agni: as great as Agni is, as great as is his measure, so great does this become.