Śatapatha Brāhmaṇa ("of a hundred paths") 9.3.1.23

9.3.1.23

atha yaṃ tṛtīyamuttarato juhoti | candāṃsi sa sa saptakapālo bhavati sapta hi caturuttarāṇi candāṃsi tamanantarhitam pūrvasmājjuhotyanantarhitāni tadṛṣibhyaścandāṃsi dadhāti

And the third (cake) which he offers on the left side, is the metres; it is one of seven potsherds, for there are seven metres increasing by four (syllables respectively). He offers it close to the preceding one: he thus places the metres close to the Rishis.