Śatapatha Brāhmaṇa ("of a hundred paths") 7.2.2.4

7.2.2.4

so 'gnerdakṣiṇāṃ śroṇim | jaghanena tiṣṭhannuttarasyāṃsasya purastādyujyamānamabhimantrayate sīrā yuñjanti kavayo yugā vitanvate pṛthagiti ye vidvāṃsaste kavayaste sīraṃ ca yuñjanti yugāni ca vitanvate pṛthagdhīrā deveṣu sumnayeti yajño vai sumnaṃ dhīrā deveṣu yajñaṃ tanvānā ityetat

Standing behind the right (southern) hip of Agni (the site of the fire-altar) he (the Pratiprasthâtri) addresses it (the plough) while being yoked (by the Adhvaryu) in front of the left (northern) shoulder, with (Vâg. S. XII, 67, 68; Rik S. X, 101, 4, 3), 'The skilful yoke the ploughs, and stretch across the yokes,'--the skilful are those who know, and they do yoke the plough and stretch the yokes across;--'the wise, with mind devoted to the gods,'--devotion means sacrifice: thus, 'the wise, performing sacrifice to the gods.'