Śatapatha Brāhmaṇa ("of a hundred paths") 2.1.4.23

2.1.4.23

athāśvamākramayati | tamākramayya prāñcamunnayati tam punarāvartayati tamudañcam pramuñcati vīryaṃ vā aśvo nedasmādidam parāgvīryamasaditi tasmātpunarāvartayati

He (the Adhvaryu) then makes the horse step on (the Âhavanîya fire-place). When he has made it step on it, he leads it out towards the east, makes it turn round again (from left to right) and lets it stand there facing the west. The horse doubtless represents strength: hence he makes it turn round again in order that this strength shall not turn away from him (the sacrificer).