Shatapatha Brahmana 1.9.1.24

1.9.1.24

atha śamyorāha | śamyurha vai bārhaspatyo 'ñjasā yajñasya saṃsthāṃ vidāṃ cakāra sa devalokamapīyāya tattadantarhitamiva manuṣyebhya āsa

Thereupon he pronounces the 'All-hail and blessing' (sam-yos). Now it was Samyu Bârhaspatya who perceived, in its true nature, the consummation of the sacrifice. He went to share in the world of the gods. Thereupon that (knowledge) was entirely lost to men.