Śatapatha Brāhmaṇa ("of a hundred paths") 1.4.4.1

1.4.4.1

taṃ vā etamagniṃ samaindhiṣata | samiddhe devebhyo juhavāmeti tasminnete eva prathame āhutī juhotī manase caiva vāce ca manaśca haiva vākca yujau devebhyo yajñaṃ vahataḥ 1.4.4[[.]]2 sa yadupāṃśu kriyate | tanmano devebhyo yajñaṃ vahatyatha yadvācā niruktaṃ kriyate tadvāgdevebhyo yajñaṃ vahatyetadvā idaṃ dvayaṃ kriyate tadete evaitatsaṃtarpayati tṛpte prīte devebhyo yajñaṃ vahāta iti

That same fire, then, they have kindled, (thinking), 'In it, when kindled, we will sacrifice to the gods.' In it, indeed, he makes these two first oblations to Mind and Speech (or, Voice); for mind and speech, when yoked together, convey the sacrifice to the gods.