Śatapatha Brāhmaṇa ("of a hundred paths") 4.4.5.2

4.4.5.2

atha samiṣṭayajūṃṣi juhoti | samiṣṭayajūṃṣi hyevānto yajñasya sa hutvaiva samiṣṭayajūṃṣi yadetamabhito bhavati tena cātvālamupasamāyanti sa kṛṣṇaviṣāṇām mekhalāṃ ca cātvāle prāsyati

In the first place he performs the Samishtayagus offerings, for the Samishtayagus are the extreme end of the sacrifice. As soon as he has performed the Samishtayagus, they go together to the kâtvâla (pit) with whatever he (the sacrificer) has about him: both the black-deer's horn and the girdle he throws into the pit,--