Śatapatha Brāhmaṇa ("of a hundred paths") 14.2.2.35

14.2.2.35

svāhā pitṛbhya ūrdhvabarhirbhyo gharmapāvabhya iti ahutvaivodaṅṅīkṣamāṇo dakṣiṇārdhe barhiṣa upagūhati yajñasya śīrṣac>innasya [raso vyakṣaratsa] pitṝ!nagacattrayā vai pitarastānevaitatprīṇātyatha yanna prekṣate sakṛdu hyeva parāñcaḥ pitaraḥ

'Hail to the Fathers, (seated) upon the Barhis, and drinking the Gharma!'--even without offering he secretes (this, the fourth stick) under the barhis of the south part (of the vedi) whilst looking towards the north. When the sacrifice had its head cut off, its life-sap flowed away, and went to the Fathers--the Fathers being three in number: it is them he thus pleases. And as to why he does not look at it,--once for all the Fathers have passed away.