Kauṣītaki (Śāṅkhāyana) Brāhmaṇa 3.8.7

3.8.7

atha yat samnayant sānnāyyasya antareṇa upāṃśv ājyasya yajati tasya uktam brāhmaṇam / (DpM)

Now, as to why, when offering the sānnāyya, he sacrifices with clarified butter in a whisper between [the offerings] of the sānnāyya, the Brāhmaṇa of that has been explained.