Śatapatha Brāhmaṇa ("of a hundred paths") 2.6.1.34

2.6.1.34

atha yataro dāsyanbhavati | yadyadhvaryurvā yajamāno vā sa udapātramādāyāpasalavi triḥ pariṣiñcanparyeti sa yajamānasya pitaramavanejayatyasāvavanenikṣvetyasāvavanenikṣveti pitāmahamasāvavanenikṣveti prapitāmahaṃ tadyathāśiṣyate 'bhiṣiñcedevaṃ tat

Now he who is about to present (the obsequial cakes to the fathers),--either the Adhvaryu or the Sacrificer,--takes the vessel of water and walks thrice round (the altar) from right to left sprinkling all about (the altar). He then, with the text, 'N.N., wash thyself!' pours out water (in the north-west corner of the altar) for the Sacrificer's father to wash himself; and (in the southwest corner), with 'N.N., wash thyself!' for the grandfather; and (in the south-east corner), with 'N.N., wash thyself!' for the great-grandfather. As one would pour out water for (a guest) who is to take food with him, so in this case.