Shatapatha Brahmana 5.1.5.21

5.1.5.21

so 'numantrayate | śaṃ no bhavantu vājino haveṣu devatātā mitadravaḥ svarkāḥ jambhayanto 'hiṃ vṛkaṃ rakṣāṃsi sanemyasmadyuyavannamīvāḥ

He then either offers or addresses (the horses) with the following tristich: this is twofold, because he either offers or addresses. Whether he offers, or addresses (the horses), the significance is the same: he thereby speeds those running horses, imbues them with energy. There are here three earths, namely this one, and two beyond it: these he thereby wins.