Śatapatha Brāhmaṇa ("of a hundred paths") 9.5.1.44

9.5.1.44

aṣṭāvasūni bhavanti | evamimāni tadyathā prāyaṇaṃtathodayanam karotisvāhākāro 'mīṣāṃ navamo bhavatyevameṣāṃ tadyathā prāyaṇaṃ tathodayanaṃ karotyāhutiramīṣāṃ daśamī bhavatyevameṣāṃ tadyathā prāyaṇaṃ tathodayanaṃ karoti saṃtatāṃ tatrāhutiṃ juhoti reto vai tatra yajño retaso 'vicedāya sruveṇeha svāhākāram niruktaṃ hi reto jāta bhavati

There are eight of those (Sâvitra), and so (there are eight of) these: thus he makes the end (the same) as the beginning. The Svâhâ-call is the ninth of those, and so it is of these: thus he makes the end as the beginning. The oblation (âhuti) is the tenth of those, and so it is of these: thus he makes the end as the beginning. On that occasion he offers the oblation continuously so as not to stop the seed, the sacrifice there being seed;--on this occasion (he offers) with the dipping-spoon at the Svâhâ-call, for manifest is the seed when it is born.