Shatapatha Brahmana 13.5.1.4

13.5.1.4

saṃsthite'gniṣṭome parihṛtāsu vasatīvarīṣvadhvaryurannahomānjuhoti teṣāmuktam brāhmaṇaṃ prāṇāya svāhāpānāya svāheti dvādaśabhiranuvākairdvādaśa māsāḥ saṃvatsaraḥ sarvaṃ saṃvatsaraḥ sarvamaśvamedhaḥ sarvasyāptyai sarvasyāvaruddhyai

When the Agnishtoma is completed, and the Vasatîvarî water carried round, the Adhvaryu performs the Annahomas (oblations of food): the import of these has been explained. With twelve Anuvâkas (Vâg. S. XXII, 23-34), 'To the in-breathing hail! To the off-breathing hail!' (he offers)--twelve months are a year, and the year is everything, and the Asvamedha is everything: thus it is for his obtaining and securing everything.