Śatapatha Brāhmaṇa ("of a hundred paths") 3.8.3.33

3.8.3.33

atha juhvā pṛṣadājyasyopaghnannāha | vanaspataye 'nubrūhītyāśrāvyāha vanaspataye preṣyeti vaṣaṭkṛte juhoti tadyadvanaspataye juhotyetamevaitadvajraṃ yūpam bhāginaṃ karoti somo vai vanaspatiḥ paśumevaitatsomaṃ karoti tadyadantareṇobhe āhutī juhoti tayobhayaṃ vyāpnoti tasmādantareṇobhe āhutī juhoti

Thereupon, while taking clotted ghee with the guhû, he says (to the Hotri), 'Recite (the invitatory prayer) to the Lord of the forest!' Having called for the Sraushat, he says (to the Maitrâvaruna), 'Prompt (the Hotri to recite the offering-prayer) to the lord of the forest!' and offers, as the Vashat is pronounced. The reason why he offers to the lord of the forest (the tree) is,--he thereby makes that thunderbolt, the sacrificial stake, a sharer (in the sacrifice); and, the lord of the forest being Soma, he thereby makes the victim to be Soma. And as to his offering (to the tree) between the two oblations, he thus fills both completely: therefore he offers between the two oblations.