Śatapatha Brāhmaṇa ("of a hundred paths") 13.8.4.6

13.8.4.6

sa y!di sthāvarā āpo bhavanti sthāpayantyeṣām pāpmānamatha yadi vahanti vahantyevaiṣām pādmānaṃ snātvāhatāni vāsāṃsi paridhāyānaḍuhaḥ pucamanvārabhyāyantyāsneyo vā anaḍvānagnimukhā eva tatpitṛlokājjīvalokamabhyāyantyatho agnirvai patho'tivoḍā sa enānativahati

And if it be standing water, it makes their (the bathers’) evil stop; and if it flows, it carries away their evil. Having bathed, and put on garments that have never yet been washed, they hold on to the tail of an ox, and return (to their home),--for the ox is of Agni's nature: headed by Agni they thus return from the world of the Fathers to the world of the living. And Agni, indeed, is he who leads one over the paths (one has to travel), and it is he who leads these over.