Kauṣītaki (Śāṅkhāyana) Brāhmaṇa 2.4.18

2.4.18

atha yad apa ācamya vratam visṛjate / (agnihotra)

ii. 4. In that, after offering, he pays reverence to the fires, verily thus having given pleasure, at the end he declares his purpose among the gods. In that also he touches the calf, therefore there is the hymn of Vātsaprī; thus cattle are not liable to stray away from the sacrificer. In that he releases his vow, after sipping water, verily in the waters he places the vow; they guard his vow until his next offering.