Śatapatha Brāhmaṇa ("of a hundred paths") 1.9.3.7

1.9.3.7

atha mukhamupaspṛśate | dvayaṃ tadyasmānmukhamupaspṛśate 'mṛtaṃ vā āpo 'mṛtenaivaitatsaṃspṛśata etadu caivaitatkarmātmaṅkurute tasmānmukhamupaspṛśate

He then touches his face (with the water in his hands). The reason why he thus touches his face is twofold: water means ambrosia, and with ambrosia he accordingly touches himself; also he thereby transfers to himself that sacred work (the sacrifice): for these reasons he touches his face.