Śatapatha Brāhmaṇa ("of a hundred paths") 9.2.2.3

9.2.2.3

atha samidha ādadhāti | yathā tarpayitvā pariveviṣyāttādṛktadaudumbaryo bhavantyūrgvai rasa udumbara ūrjaivainametadrasena prīṇātyārdrā bhavantyetadvai vanaspatīnāmanārtaṃ jīvaṃ yadārdraṃ tadyadeva vanaspatīnāmanārtaṃ jīvaṃ tenainametatprīṇāti ghṛte nyuttā bhavantyāgneyaṃ vai ghṛtaṃ svenaivainametadbhāgena svena rasena prīṇāti sarvāṃ rātriṃ vasanti tatra hi tā rasena sampadyante tisraḥ samidha ādadhāti trivṛdagniryāvānagniryāvatyasya mātrā tāvataivainametadannena prīṇāti

He then puts on the pieces of firewood: this is as if, after regaling some one, one were to attend upon him. They are of udumbara (ficus glomerata) wood; for the Udumbara is food and sap: with food and sap he thus regales him. They are fresh (green), for that part of trees which is fresh is uninjured and living: he thus regales him with what is uninjured and living in trees. They are soaked in ghee; for ghee is sacred to Agni: with his own portion, with his own sap he thus regales him. They remain the whole night in it, for there they become imbued with sap. Three pieces of wood he puts on,--threefold is Agni: as great as Agni is, as great as is his measure, with so much food he thus regales him.