Shatapatha Brahmana 11.2.5.5

11.2.5.5

taṃ vā etam māsi-māsyevāśvamedhamālabhante sa yo haivaṃ vidvānagnihotraṃ ca juhoti darśapūrṇamāsābhyāṃ ca yajate māsi-māsi haivāsyāśvamedheneṣṭam bhavatyetadu hāsyāgnihotraṃ ca darśapūrṇamāsau cāśvamedhamabhisampadyete

Verily, then, for him who, knowing this, offers both the Agnihotra and the Full and New-moon sacrifices, they slaughter the sacrificial horse month by month; and month by month the Asvamedha is offered for him, and his Agnihotra and Full and New-moon sacrifices come to pass into the Asvamedha.