Śatapatha Brāhmaṇa ("of a hundred paths") 13.1.2.3

13.1.2.3

abhidhā asīti tasmādaśvamedhayājī sarvā diśo'bhijayati bhuvanamasīti bhuvanaṃ tajjayati yantāsi dharteti yantāramevainaṃ dhartāraṃ karoti sa tvamagniṃ vaiśvānaramityagnimevainaṃ vaiśvānaraṃ gamayati saprathasaṃ gaceti prajayaivainam paśubhiḥ prathayati svāhākṛta iti vaṣaṭkāra evāsyaiṣa svagā tvā devebhya iti devebhya evainaṃ svagā karoti prajāpataya iti prājāpatyo'śvaḥ svayaivainaṃ devatayā samardhayati

[He puts the halter on the horse, with Vâg. S. XXII, 3, 4,] 'Encompassing thou art,'-- therefore the offerer of the Asvamedha conquers all the quarters;--'the world thou art,'--the world he thus conquers;--'a ruler thou art, an upholder,'--he thus makes him a ruler and upholder;--'go thou unto Agni Vaisvânara,'--he thus makes him go to Agni Vaisvânara (the friend of all men);--'of wide extent,'--he thus causes him to extend in offspring and cattle;--'consecrated by Svâhâ (hail!),'--this is the Vashat-call for it;--'good speed (to) thee for the gods!'--he thus makes it of good speed for the gods;--'for Pragâpati,'--the horse is sacred to Pragâpati: he thus supplies it with his own deity.