Shatapatha Brahmana 9.5.1.30

9.5.1.30

te vā ete nava yajñāḥ | navaitāni samiṣṭayajūṃṣi tadyadetāni juhotyetānevaitadyajñāntsaṃsthāpayatyubhayāni juhotyadhvarasya cāgneścādhvarasya pūrvāṇyathāgnestasyokto bandhuḥ

Now there are nine such (incomplete) sacrifices, and there are nine samishtayagus-oblations; and by offering these, he completes those sacrifices. He offers both kinds, those of the Soma-sacrifice, and those of the Agni(-kayana),--first those of the Soma-sacrifice, and afterwards those of the fire-altar: the significance of this has been explained.