Shatapatha Brahmana 8.5.1.17

8.5.1.17

sa yaddha vā evaṃvitprāṇiti | yo 'sya purastātpāpmā bhavati taṃ tenāpahate 'tha yadapāniti tena taṃ yaḥ paścādatha yadbāhubhyāṃ karma kurute tena taṃ yo 'bhito 'tha yadannamatti tena taṃ ya upariṣṭātsarvadā ha vā evaṃvitpāpmānamapahate 'pi svapaṃstasmādevaṃ viduṣaḥ pāpaṃ na kīrtayennedasya pāpmāsānīti

And, verily, whenever he, knowing this, breathes out, he thereby drives away the evil which is in front of him; and when he breathes backward, he thereby (drives away) that which is in the rear; and when he does work with his arms, he thereby (drives away) that which is sideways of him; and when he eats food, he thereby (drives away) that (evil) which is above him: at all times, indeed, even while sleeping, does he who knows this drive away evil. Hence, one must not speak ill of him who knows this, lest one should be his evil (enemy).