Shatapatha Brahmana 4.1.1.19

4.1.1.19

sa vā antareva santsvāheti karoti | devā ha vai bibhayāṃ cakruryadvai naḥ puraivāsya grahasya homādasurarakṣasānīmaṃ grahaṃ na hanyuriti tamantareva santaḥ svāhākāreṇājuhavustaṃ hutameva santamagnāvajuhavustatho evainameṣa etadantareva santsvāhākāreṇa juhoti taṃ hutameva santamagnau juhoti

While he is still inside (the Havirdhâna) he utters 'Hail!' For the gods were afraid lest the Asura-Rakshas should destroy what part of this graha was previous to the offering. They offered it (symbolically) by means of the Svâhâ, while they were still inside (the cart-shed), and what was thus offered they afterwards offered up in the fire. And in like manner does he now offer it up by means of the Svâhâ, while he is still inside, and what has thus been offered he afterwards offers up in the fire.