Shatapatha Brahmana 10.4.1.16

10.4.1.16

sa eṣa saṃvatsaraḥ prājāpatiragniḥ tasyārdhameva sāvitrāṇyardhaṃ vaiśvakarmaṇānyaṣṭāvevāsya kalāḥ sāvitrāṇyaṣṭau vaiśvakarmaṇānyatha yadetadantareṇa karma kriyate sa eva saptadaśaḥ prajāpatiryo vai kalā manuṣyāṇāmakṣaraṃ taddevānām

And this Agni is Pragâpati, the year: the Sâvitra (oblations) are one half thereof, and the Vaisva-karmana (oblations) the (other) half; the Sâvitra are eight digits (kalâ) thereof, and the Vaisvakarmana (the other) eight; and that which is performed between them is the seventeenfold Pragâpati. Now what a digit is to men that a syllable (akshara) is to the gods.