Śatapatha Brāhmaṇa ("of a hundred paths") 2.5.1.10

2.5.1.10

atha sāvitraḥ | dvādaśakapālo vāṣṭākapālo vā puroḍāśo bhavati savitā vai devānām prasavitā prajāpatirmadhyataḥ prajanayitā tasmātsāvitro bhavati

Then follows a cake on twelve or eight potsherds for Savitri. Savitri indeed is the impeller (pra-savitri) of the gods; he is Pragâpati, the intermediate progenitor: hence the cake to Savitri.