Śatapatha Brāhmaṇa ("of a hundred paths") 9.4.2.11

9.4.2.11

sa dakṣiṇāyugyamevāgre yunakti | atha savyāyugyamatha dakṣiṇāpraṣṭimevaṃ devatretarathā mānuṣe taṃ nābhiyuñjyānnedyuktamabhiyunajānīti vāhanaṃ tu dadyādyuktena bhunajā iti tamuparyeva harantyādhvaryorāvasathādupari hyeṣa tamadhvaryave dadāti sa hi tena karoti taṃ tu dakṣiṇānāṃ kāle 'nudiśet

The right yoke-horse he puts to first, then the left yoke-horse, then the right side-horse: for thus it is (done) among the gods, otherwise in human (practice). Let him not yoke that (chariot) again, lest he should yoke again the yoked one; but let him give away the vehicle, thinking, 'I shall reap the benefit of the yoking of it.' They carry it as far as the Adhvaryu's dwelling, holding it right upwards, for above is that (Agni). He presents it to the Adhvaryu, for it is he that performs therewith. Let him, however, (not) assign it to him (till) the time of the offering-gifts.