100 tiny white beads in a silk bag.
If you swallow one of these beads and get a good night's sleep, you will be clean when you wakes up, and for one hour afterward. Ingesting two beads at the same time will produce instant cleanliness which lasts for one hour, but you will have disadvantage on constitution saving throws until the next time you complete a long rest.
Each bead, when swallowed before a good night's sleep, has the same effect as a paladin's ability to be perpetually clean. The imbiber is clean when he wakes up, and for one hour afterward. Ingesting two beads at the same time will produce instant cleanliness which lasts for one hour, but results in 1 CON damage. This damage goes away after a good night's sleep, and cannot be otherwise cured by anything short of Greater Restoration. The CON damage does not stack with itself.
The wizard Elmeraer got these from an old friend and party member, a paladin who had lost his powers and didn't want anyone to know. He ended up using about thirty of the original hundred, most of which taken two at a time.