Śatapatha Brāhmaṇa ("of a hundred paths") 5.1.5.6

5.1.5.6

athaiteṣāṃ dundubhīnām | ekaṃ yajuṣāhanti tatsarve yajuṣāhatā bhavanti

They put up seventeen drums along the edge of the altar, from the Âgnîdhra backwards (towards the west); for he who offers the Vâgapeya wins Pragâpati; but Pragâpati is speech, and that doubtless is the supreme speech which is (the outcome) of seventeen drums: he thus wins the supreme speech, the supreme Pragâpati. Seventeen there are, because Pragâpati is seventeenfold: he thus wins Pragâpati.