Śatapatha Brāhmaṇa ("of a hundred paths") 4.2.4.15

4.2.4.15

yadvā asyāvācīnaṃ nābheḥ | tadasyaiṣa ātmano 'dha iva vai tadyadavācīnaṃ nābheradha ivaitadya dvyuhya na tṛṇaṃ canāntardhāya tasmādetaṃ vyuhya na tṛṇaṃ canāntardhāya sādayati

For this (cup of Soma) is that part of his body from the navel downwards; and below, as it were, is what is from the navel downwards; and below, as it were, is what (one deposits) after pushing (the dust) aside and leaving not so much as a blade of grass between: therefore he deposits this (Dhruva graha) after pushing (the dust) aside, without leaving so much as a blade of grass between.