Śatapatha Brāhmaṇa ("of a hundred paths") 5.1.5.3

5.1.5.3

triḥ sāmābhigāyati | trirabhigīyāvarohati devasyāhaṃ savituḥ save satyaprasavaso bṛhaspateruttamaṃ nākamaruhamiti yadi brāhmaṇo yajate brahma hi bṛhaspatirbrahma hi brāhmaṇaḥ

And if a Râganya sacrifices, (he does so) with, 'At the impulse of the divine Savitri, of true impulsion, may I ascend unto the highest heaven of Indra!' for Indra is the Kshatra (nobility, or power), and the Râganya is the Kshatra.