Śatapatha Brāhmaṇa ("of a hundred paths") 1.4.4.13

1.4.4.13

sa sruveṇa pūrvamāghāramāghāryāha | agnimagnītsammṛḍhīti yathā dhuramadhyūhedevaṃ tadyatpūrvamāghāramāghāray3atyadhyuhya hi dhuraṃ yuñjanti

When he has made the first libation with the dipping-spoon, he says, 'Agnîdh, sweep (touch over) the fire!' In like manner as one would lay the yoke on (the shoulders of the team), so also he makes that first libation; for after laying on the yoke they fasten (the team to it).