Shatapatha Brahmana 13.5.1.15

13.5.1.15

saptadaśaiva paśūnmadhyame yūpa ālabhet prajāpatiḥ saptadaśaḥ sarvaṃ saptadaśaḥ sarvamaśvamedhaḥ sarvasyāptai sarvasyāvarudhyai ṣoḍaśa ṣoḍaśetareṣu ṣoḍaśkalam vā idaṃ sarvaṃ sarvamaśvamedhaḥ sarvasyāptai sarvasyāvarudhyai trayodaśa trayodaśāraṇyānākāśeṣvālabhate trayodaśa māsāḥ samvatsaraḥ sarvaṃ samvatsaraḥ sarvamaśvamedhaḥ sarvasyāptai sarvasyāvarudhyai

Let him seize seventeen victims for the central stake, in order that he may gain and secure every-thing, for the seventeenfold is Pragâpati, and the seventeenfold (stoma) is everything, and the Asvamedha is everything;--and sixteen at each of the other (stakes) in order that he may gain and secure everything, for everything here consists of sixteen parts, and the Asvamedha is everything. Thirteen wild (beasts) he seizes for each intermediate space, in order that he may gain and secure everything, for the year consists of thirteen months, and the Asvamedha is everything.