Śatapatha Brāhmaṇa ("of a hundred paths") 5.1.4.5

5.1.4.5

athāśvānadbhirabhyukṣati | snapanāyābhyavanīyamānāntsnapitānvodānītānadbhyo ha vā agre 'śvaḥ sambabhūva so 'dbhyaḥ sambhavannasarvaḥ samabhavadasarvo hi vai samabhavattasmānna sarvaiḥ padbhiḥ pratitiṣṭhatyekaikameva pādamudacya tiṣṭhati tadyadevāsyātrāpsvahīyata tenaivainametatsamardhayati kṛtsnaṃ karoti tasmādaśvānadbhirabhyukṣati snapanāyābhyavanīyamānāntsnapitānvodānītān

He then sprinkles the horses with water, either when being led down to be watered, or when brought up after being watered. Now in the beginning the horse was produced from the water; while being produced from the water, it was produced incomplete, for it was indeed produced incomplete: hence it does not stand on all its feet, but it stands lifting one foot on each side. Thus what then was left behind of it in the water, therewith he now completes it, and makes it whole: therefore he sprinkles the horses with water, either when being led down to be watered, or when brought up after being watered.