Shatapatha Brahmana 14.3.1.25

14.3.1.25

athainamadbhiḥ pariṣiñcati śāntirvā āpaḥ śamayatyevainametatsarvataḥ pariṣiñcati sarvata evainametacamayati triṣkṛtvaḥ pariṣiñcati trivṛddhi yajñaḥ

He then sprinkles it (the Pravargya apparatus) with water: water being a means of appeasement, he thus appeases it; he sprinkles it all over: all over he thus appeases it; three times he sprinkles, for threefold is the sacrifice.