Śatapatha Brāhmaṇa ("of a hundred paths") 4.6.7.20

4.6.7.20

tadvā etanmano 'dhvaryuḥ | pura ivaiva carati tasmātpuraścaraṇaṃ nāma pura iva ha vai śriyā yaśasā bhavati ya evametadveda

Thus, then, the Adhvaryu, the mind, walks, as it were, in front (puras-karati): hence the name 'puraskarana;' and verily, he who knows this, stands, as it were, in front through prosperity and glory.