Śatapatha Brāhmaṇa ("of a hundred paths") 13.2.3.2

13.2.3.2

yadudgātodgāyet yathākṣetrajño'nyena pathā nayettādṛktadatha yadudgātāramavarudhyāśvamudgīthāya vṛṇīte yathā kṣetrajño'ñjasā nayedevamevaitadyajamānamaśvaḥ svargaṃ lokamañjasā nayati hiṅkaroti sāmaiva taddhiṅkarotyudgītha eva sa vaḍavā uparundhanti saṃśiñjate yathopagātāra upagāyanti tādṛktaddhiraṇyaṃ dakṣiṇā suvarṇaṃ śatamānaṃ tasyoktam brāhmaṇam

Were the Udgâtri to chant the Udgîtha, it would be even as if one who does not know the country were to lead by another (than the right) way. But if, setting aside the Udgâtri, he chooses the horse for (performing) the Udgîtha, it is just as when one who knows the country leads on the right way: the horse leads the Sacrificer rightly to the heavenly world. It makes 'Hiṅ,' and thereby makes the. Sâman itself to be 'hiṅ': this is the Udgîtha. They pen up mares, (and on seeing the horse) they utter a shrill sound: as when the chanters sing, such like is this. The priests’ fee is gold weighing a hundred (grains): the mystic import of this has been explained.