Śatapatha Brāhmaṇa ("of a hundred paths") 11.2.1.6

11.2.1.6

tāḥ pañcadaśāhutayaḥ tāsām pañcadaśānāmāhutīnāmetā anuvākyā etāḥ pañcadaśa sāmidhenya etāsāmanuvākyānāmetā yājyā ya evātra mantro yo nigadastadyājyārūpameteno hāsyaitā āhutayo'nuvākyavatyo bhavantyetābhiḥ sāmidhenībhiretābhirāhutibhiretā anuvākyā yājyavatyaścāhutivatyaśca bhavanti

That makes fifteen oblations:--for these fifteen oblations those fifteen kindling-verses (serve, as it were, as) invitatory formulas; and for these invitatory formulas these (serve as) offering-formulas--whatever formula (is used) there (at those oblations) and what Nigada (is used at the invocation of the Idâ) that is of the form of offering-formulas. Thereby, then, those oblations of his come to be supplied with invitatory formulas through those kindling-verses; and through those oblations those invitatory formulas come to be supplied with both offering-formulas and oblations.