Shatapatha Brahmana 8.5.1.14

8.5.1.14

sā yā purastātprāṇaḥ sā | yā paścādapānaḥ sā prāṇenaiva tatpurastātpāpmānamapāhatāpānena paścāttathaivaitadyajamānaḥ prāṇenaiva purastātpāpmānamapahate 'pānena paścāt

The one which (lies) in front is the out-breathing, the one at the back the off-breathing: by the out-breathing he (Pragâpati) then drove away evil in front, and by the off-breathing in the rear; and in like manner does the Sacrificer now by the out-breathing drive away evil in front, and by the off-breathing in the rear.