Śatapatha Brāhmaṇa ("of a hundred paths") 13.2.2.13

13.2.2.13

saptadaśaiva paśūnmadhyame yūpa ālabheta saptadaśo vai prajāpatim prajāpatiraśvamedho'śvamedhasyaivāptyai ṣoḍaśa ṣoḍaśetareṣu ṣoḍaśakalaṃ vā idaṃ sarvaṃ tadidaṃ sarva mavarunddhe

Let him rather bind seventeen animals to the central stake; for seventeenfold is Pragâpati, and the Asvamedha is Pragâpati,--thus for the obtainment of the Asvamedha. And sixteen (victims he binds) to each of the other (stakes), for of sixteen parts (kalâ) consists all this (universe); all this (universe) he thus gains.