Skandapurana 6.3.220.27

6.3.220.27

agniśca tejo mṛḍayā ca deho reto'dhā viṣṇuramṛtasya nābhiḥ .
evaṃ bruvan pāṇḍava satyavākyaṃ tato'vagāheta patiṃ nadīnām .
iti snānamantraḥ .. 220.27 ..

"Fire is fiery energy, through Mṛḍā is the body, Viṣṇu is the holder of the seed, the navel of immortality." / Speaking this true utterance, O Pāṇḍava, one should then plunge into the lord of rivers. / This is the bathing mantra.