Shatapatha Brahmana 7.4.1.42

7.4.1.42

athaudumbarīmuttarata upadadhāti | indrasya tvaujasā sādayāmīti yadevāsya tadindra oja ādāyodaṅṅudakrāmattadasminnetatpratidadhāti bhuvo yajñasya rajasaśca netetyeṣa u sa indraḥ sā yadāgneyyagnikarma hyatha yattriṣṭuptraiṣṭubho hīndra aindrāgno 'gniryāvānagniryāvatyasya mātrā tāvataivaināmetadupadadhātīndrāgnī vai sarve devāḥ sarvadevatyo 'gniryāvānagniryāvatyasya mātrā tāvataivaināmetadupadadhāti dadhnā pūrṇā bhavatyaindraṃ vai dadhi svenaivainametadbhāgena svena rasena prīṇāti

He then lays down the udumbara one on the left (north) side, with (Vâg. S. XIII, 14), 'By Indra's vigour I settle thee!' that vigour of his (Pragâpati's) which Indra then took and went away to the north, he now puts back into him.--(Vâg. S. XIII, 15; Rik S. X, 8, 6), 'Thou hast become the leader of the sacrifice, and of the sphere to which thou tendest with propitious teams; the light-giving head hast thou lifted to the sky; thy tongue, O Agni, hast thou made the bearer of the offering;'--Indra indeed is this (spoon). And as to its being a verse addressed to Agni, it is because it is the performance of Agni (the fire-altar);--and a trishtubh one, because Indra is connected with the Trishtubh; and Agni includes Indra and Agni: as great as Agni is, as great as is his measure, with so much he thus lays it down. Moreover, all the gods are Indra and Agni, and Agni belongs to all the deities: as great as Agni is, as great as is his measure, with so much he thus lays it down. It is filled with sour curds, for sour curds belong to Indra: with his own share, with his own life-sap he thus gratifies him.