Shatapatha Brahmana 1.9.2.32

1.9.2.32

atha praṇītā dakṣiṇataḥ parītya ninayati | yuṅkte vā etadyajñaṃ yadenaṃ tanute sa yanna ninayetparāṅu hāvimukta eva yajño yajamānam prakṣiṇīyāttatho ha yajño yajamānaṃ na prakṣiṇāti tasmātpraṇītā dakṣiṇataḥ parītya ninayati

Having thereupon walked round (from the north side of the Âhavanîya fire) to the south, he pours the pranîtâ-water out (on the altar). Now, when he spreads the sacrifice, he yokes it. But were he not to pour out (the pranîtâ-water), the sacrifice, being unyoked, would, in moving backward, injure the sacrificer. In this way, however, the sacrifice does not injure the sacrificer; and for this reason he pours out the pranîtâ-water, after walking round to the south.