Shatapatha Brahmana 13.1.4.1

13.1.4.1

prajāpatiraśvamedhamasṛjata so'smātsṛṣṭaḥ parāṅaitsa diśo'nuprāviśattaṃ devāḥ praiṣamaicaṃstamiṣṭibhiranuprāyuñjata tamiṣṭibhiranvaicaṃstamiṣṭibhiranvavindanyadiṣṭibhiryajate'śvameva tanmedhyaṃ yajamāno'nvicati

Pragâpati poured forth the life-sap of the horse (asva-medha). When poured forth, it went straight away from him and spread itself over the regions. The gods went in quest of it. By means of offerings (ishti) they followed it up, by offerings they searched for it, and by offerings they found it. And when he performs ishtis, the Sacrificer thereby searches for the horse (asva) meet for sacrifice (medhya).