Śatapatha Brāhmaṇa ("of a hundred paths") 4.6.6.5

4.6.6.5

sa hovāca | kim me tataḥ syāditi brāhmaṇācaṃsyā te brahmasāma ta iti tasmādbrāhmaṇācaṃsinam pravṛṇīta indro brahmā brāhmaṇāditīndrasya hyeṣā sa indro dakṣiṇata āstāthābhaye nāṣṭra uttarato yajñamupācaraṃstasmādya eva vīryavattamaḥ syātsa dakṣiṇata āsītātābhaye 'nāṣṭra uttarato yajñamupacareyuryo vai brāhmaṇānāmanūcānatamaḥ sa eṣāṃ vīryavattamo 'tha yadidaṃ ya eva kaśca brahmā bhavati kuvittūṣṇīmāsta iti tasmādya eva vīryavattamaḥ syātsa dakṣiṇata āsītāthābhaye 'nāṣṭra uttarato yajñamupacareyustasmādbrāhmaṇā dakṣiṇata āsate 'thābhaye 'nāṣṭra uttarato yajñamupacaranti

He said, 'What will be my reward then?'--'The office of Brâhmanâkhamsin shall be thine, the Brahmasâman shall be thine!'--Hence one elects the Brâhmanâkhamsin with, 'Indra is the Brahman, by virtue of the Brahmaship!' for to Indra belongs this (office). Indra sat on the south side, and they entered upon the sacrifice on the north side in a place free from danger and injury. Therefore let him who is the strongest sit on the south side, and let them then enter upon the sacrifice on the north side in a place free from danger and injury. Now he, forsooth, who is the most learned of Brâhmans, is the strongest of them; and as now any one is (able to become) a (superintendent) Brahman --nay, does he not sit still?--therefore whosoever is the strongest of them, let him sit on the south side, and let them then enter upon the sacrifice on the north side in a place free from danger and injury. Hence Brâhmans sit on the south side (of the vedi), and they enter upon the sacrifice on the north side in a place free from danger and injury.