Shatapatha Brahmana 9.1.2.36

9.1.2.36

rathantaraṃ dakṣiṇe pakṣe | iyaṃ vai rathantaramiyamu vā eṣāṃ lokānāṃ rasatamo 'syāṃ hīme sarve rasā rasaṃtamaṃ ha vai tadrathantaramityācakṣate paro 'kṣam paro 'kṣakāmā hi devā imāmevāsyaitaddakṣiṇam pakṣaṃ karotyatho dakṣiṇamevāsyaitatpakṣamanasthikamamṛtaṃ karoti

The Rathantara (hymn he sings) at the right wing; for the Rathantara is this (earth), and this (earth), doubtless, is the most essential (rasatama) of these worlds, for it is in her that all these essences (rasa) are contained, and 'rasantama,' indeed, they call mystically, 'rathantara,' for the gods love the mystic: he thus makes this (earth) his right wing, and that right wing of his he thus makes boneless and immortal.