Śatapatha Brāhmaṇa ("of a hundred paths") 6.2.2.25

6.2.2.25

yadvevāṣṭakāyām | aṣṭakā vā ukhā nidhirdvā uddhī tiraścī rāsnā taccatuścitasra ūrdhvāstadaṣṭāvaṣṭakāyāmeva tadaṣṭakāṃ karoti

And, again, why on the eighth day;--eightfold doubtless is the pan --the bottom part, the two side-parts, the horizontal belt (or rim), that makes four; and four upright (bands), that makes eight: he thus makes the eightfold on the eightfold (or eighth).