Śatapatha Brāhmaṇa ("of a hundred paths") 5.3.1.3

5.3.1.3

atha śvo bhūte | sūyamānasya gṛha aindramekādaśakapālam puroḍāśaṃ nirvapati kṣatraṃ vā indraḥ kṣatraṃ sūyamānastasmādaindro bhavati tasyarṣabho dakṣiṇā sa hyaindro yadṛṣabhaḥ

And on the following day he prepares a cake on eleven potsherds for Indra at the dwelling of him who is being consecrated (the king); for Indra is the Kshatra (ruling power), and he who is consecrated is the Kshatra: hence it is for Indra. The sacrificial fee for this is a bull, for the bull is Indra's own (animal).