Śatapatha Brāhmaṇa ("of a hundred paths") 1.2.2.11

1.2.2.11

tamadbhirabhimṛśati | sakṛdvā trirvā tadyadevāsyātrāvaghnanto vā piṃṣanto vā kṣiṇvanti vā vi vā vṛhanti śāntirāpastadadbhiḥ śāntyā śamayati tadadbhiḥ saṃdadhāti tasmādadbhirabhimṛśati

He then touches it over with water, either once or three times: for whatever in this (rice-offering) they either injure or tear asunder in the threshing or grinding of it, that--water being (a means of) expiation (or purification)--he thereby expiates with water, that is, with (the means of) expiation; that he thereby makes good: for this reason he touches it over with water.