Shatapatha Brahmana 7.2.2.21

7.2.2.21

athainānvimuñcati | āptvā taṃ kāmaṃ yasmai kāmāyainānyuṅkte vimucyadhvamaghnyā ityaghnyā haite devatrā devayānā iti daivaṃ hyebhiḥ karma karotyaganma tamasaspāramasyetyaśanāyā vai tamo 'ganmāsyā aśanāyāyai pāramityetajjyotirāpāmeti jyotirhyāpnoti yo devānyo yajñamathainānudīcaḥ prācaḥ prasṛjati tasyokto bandhustānadhvaryave dadāti sa hi tai karoti tāṃstu dakṣiṇānāṃ kāle 'nudiśet

Having gained the object for which he yokes those (oxen), he now unyokes them, with (Vâg. S. XII, 73), 'Be ye unyoked, ye inviolable (oxen)!' for inviolable they indeed are with the gods;--'Ye god ward-striding!' for with them he performs the divine work;--'We have come to the end of this gloom;'--gloom doubtless means famine: thus, 'we have come to the end of this famine;'--'we have attained the light!' for he who attains the gods, the sacrifice, indeed attains the light. He then lets them loose towards north-east--the significance of this has been explained. He gives them to the Adhvaryu, for it is he that does the work with them: let him assign them (to him) at the time of (the presentation of) the Dakshinâs.