Śatapatha Brāhmaṇa ("of a hundred paths") 1.8.2.8

1.8.2.8

atha yadanuyājānyajati | candāṃsi vā anuyājāḥ paśavo vai devānāṃ candāṃsi tadyathedaṃ paśavo yuktā manuṣyebhyo vahantyevaṃ candāṃsi yuktāni devebhyo yajñaṃ vahanti tadyatra candāṃsi devāntsamatarpayannatha candāṃsi devāḥ samatarpayaṃstadatastatprāgabhūdyaccandāṃsi yuktāni devebhyo yajñamavākṣuryadenāntsamatītṛpan

Now this is why he makes the after-offerings. The after-offerings assuredly are the metres, and the metres are the cattle of the gods: hence as cattle, when harnessed, here convey (burdens) for men, so in like manner the metres, being harnessed, convey the sacrifice to the gods. Now the occasion on which the metres gratified the gods, and for which the gods, in their turn, then gratified the metres, was when before this the metres, on being harnessed, conveyed the sacrifice to the gods and thereby gratified them.