Garudapurana 1.213.143

1.213.143

snāne caritamityetatsamuddiṣṭaṃ mahātmabhiḥ /
brahmakṣatraviśāṃ caiva mantravatsnānamiṣyate //

This is declared by the great-souled ones as the conduct observed in bathing. / For Brahmins, Kṣatriyas, and Vaiśyas, the bath is prescribed with mantras;