Verse 5.1.5.27

athaiteṣāmājiśritāṃ rathānām | ekasminvaiśyo vā rājanyo vopāsthito bhavati sa vederuttarāyāṃ śroṇā upaviśatyathādhvaryuśca yajamānaśca pūrvayā dvārā madhugrahamādāya niṣkrāmatastaṃ vaiśyasya vā rājanyasya vā prāṇāvādhatto'tha neṣṭāparayā dvārā surāgrahānādāya niṣkrāmati sa jaghanena śālām paryetyaikaṃ vaiśyasya vā rājanyasya vā prāṇāvādadhadāhānena ta imaṃ niṣkrīṇāmīti satyaṃ vai śrīrjyotiḥ somo'nṛtam pāpmā tamaḥ surā satyamevaitacriyaṃ jyotiryajamāne dadhātyanṛtena pāpmanā tamasā vaiśyaṃ vidhyati taiḥ sa yam bhogaṃ kāmayate taṃ kurute'thaitaṃ sahiraṇyapātrameva madhugraham brahmaṇe dadāti tam brahmaṇe dadadamṛtamāyur ātmandhatte'mṛtaṃ hyāyurhiraṇyaṃ tena sa yam bhogaṃ kāmayate taṃ kurute

Preview of English translation:

27. He makes the horses smell it, with, “Ye coursers!” for horses are coursers: therefore he says, “Ye coursers! wealth-winners!” wealth is food: “food-winners” he thereby says;—“having run the course—” for 'starting (upon the course)' he said before, as then they were indeed starting; but now he says, “having run,” for they indeed have run (the race): therefore he says, “having run;”—“smell ye Brihaspati’s portion—” for this is Brihaspati’s portion: therefore he says, “Smell ye Brihaspati’s portion;”—“taking (it) in!” whereby. he imbues the Sacrificer with energy. And as to why he makes the horses smell,—he made them smell before, thinking, “May I win this (world);” and now (he does so) thinking, 'I have won this (world) that is why he makes the horses smell.

For a detailled translation, including proper diacritics and footnotes, go the full English translation.