Śatapatha Brāhmaṇa ("of a hundred paths") 3.8.1.5

3.8.1.5

atha yūpaśakalamādatte | tāvagre juhvā aktvā paśorlalāṭamupaspṛśati ghṛtenāktau paśūṃstrāyethāmiti vajro vai yūpaśakalo vajraḥ śāso vajra ājyaṃ tamevaitatkṛtsnaṃ vajraṃ sambhṛtya tamasyābhigoptāraṃ karoti nedenaṃ nāṣṭrā rakṣāṃsi hinasanniti punaryūpaśakalamavagūhatyeṣā te prajñātāśrirastvityāha śāsam prayacantsādayati srucau

He then takes the (svaru) chip of the sacrificial stake, and having anointed both (the slaughtering-knife and the chip) at the top (with ghee) from the guhû-spoon, he touches the forehead of the victim with them, saying (Vâg. S. VI, 11), 'Anointed with ghee, protect ye the animals!' for the chip of the stake is a thunderbolt, and the slaughtering-knife is a thunderbolt, and ghee is a thunderbolt; having thus fitted together the entire thunderbolt he appoints it the keeper of this (victim), lest the evil spirits should injure it. He again conceals the chip of the stake (under the girding-rope of the stake). In handing the slaughtering-knife to the butcher, he says, 'Be this thine approved edge!' and deposits the two spoons.