Śatapatha Brāhmaṇa ("of a hundred paths") 13.4.2.17

13.4.2.17

sa āhāśāpālāḥ ye vā etasyodṛcaṃ gamiṣyanti rāṣṭraṃ te bhaviṣyanti rājāno bhaviṣyantyabhiṣecanīyā atha ya etasyodṛcaṃ na gamiṣyantyarāṣṭraṃ te bhaviṣyantyarājāno bhaviṣyanti rājanyā viśo'nabhiṣecanīyāstasmānmā pramadata snātvāccaivainamudakānnirundhīdhvaṃ vaḍavābhyaśca te yadyadbrāhmaṇajātamupanigaceta tattatpṛceta brāhmaṇāḥ kiyadyūyamaśvamedhasya vittheti te ye na vidyurjinīyāta tāntsarvaṃ vā aśvamedhaḥ sarvasyaiṣa na veda yo brāhmaṇaḥ sannaśvamedhasya na veda so'brāhmaṇo jyeya eva sa pānaṃ karavātha khādaṃ nivapāthātha yatkiṃ ca janapade kṛtānnaṃ sarvaṃ vastatsutaṃ teṣāṃ rathakārakula eva vo vasatistaddhyaśvasyāyatanamiti

He says, 'Ye guardians of the quarters, those who go on to the end of this (horse-sacrifice) will become (sharers of) the royal power, they will become kings worthy of being consecrated; but those who do not go on to the end of this (sacrifice) will be excluded from royal power, they will not become kings, but nobles and peasants, unworthy of being consecrated: do not ye therefore be heedless, and keep it (the horse) from water suitable for bathing and from mares! And whenever ye meet with any kind of Brâhmanas, ask ye them, "O Brâhmanas, how much know ye of the Asvamedha?" and those who know naught thereof ye may despoil; for the Asvamedha is everything, and he who, whilst being a Brâhmana, knows naught of the Asvamedha, knows naught of anything, he is not a Brâhmana, and as such liable to be despoiled. Ye shall give it drink, and throw down fodder for it; and whatever prepared food there is in the country all that shall be prepared for you. Your abode shall be in the house of a carpenter of these (sacrificers), for there is the horse's resting-place.'