Śatapatha Brāhmaṇa ("of a hundred paths") 1.3.2.15

1.3.2.15

tadāhuḥ | kasmā u tarhyupabhṛti gṛhṇīyādyadupabhṛtā na juhotīti sa yaddhopabhṛtā juhuyātpṛthagghaivemāḥ prajāḥ syurnaivāttā syānnādyaḥ syādatha yattajjuhveva samānīya juhoti tasmādimā viśaḥ kṣatriyasyaiva vaśe sati vaiśyam paśava upatiṣṭante 'tha yattajjuhveva samānīya juhoti tasmādyadota kṣatriyaḥ kāmayate 'thāha vaiśya mayi yatte paro nihitaṃ tadāhareti taṃ jināti tvadyathā tvatkāmayate tathā sacata eteno hatadvīryeṇa

And in reference to this point they say: 'Wherefore then is he to take it in the upabhrit, if he does not offer it with the upabhrit?' Now, if he were to offer it with the upabhrit, those subjects (of the king) would assuredly become separated from him, nor would there be either an eater or what is to be eaten. When, on the other hand, he pours (the butter) together and thus offers it with the guhû, thereby the people pay tribute to the Kshatriya. Hence by what he takes in the upabhrit, the Vaisya (man of the people), under the rule of the Kshatriya, becomes possessed of cattle; and when he pours (the butter) together and offers it with the guhû, thereby the Kshatriya, whenever he likes, says, 'Hallo Vaisya, just bring to me what thou hast stored away!' Thus he both subdues him and obtains possession of anything he wishes by dint of this very energy.