Śatapatha Brāhmaṇa ("of a hundred paths") 13.5.3.9

13.5.3.9

tasya trivṛdbahiṣpavamānam pañcadaśānyājyāni saptadaśo mādhyandinaḥ pavamāna ekaviṃśāni pṛṣth\āni triṇavastṛtīyaḥ pavamānastrayastriṃśamagniṣṭomasāmaikaviṃśānyukthānyekaviṃśaḥ ṣoḍaśī pañcadaśī rātristrivṛtsandhiryaddvitīyasyāhnaḥ pṛṣth\yasya ṣaḍahasya tacastramatirātro yajñastenāmuṃ lokamṛdhnoti

But concerning this, Sâtyayagñi said, 'They may indeed do it in either way, only one must not depart from the (right) path.' But the former, indeed, is the established practice. The sacrifice (of the second day) is an Ukthya: thereby he causes the air-world to prosper. The last day is an Atirâtra with all the Stomas, for him to obtain and secure everything, for the Atirâtra with all the Stomas is everything, and the Asvamedha is everything.