Bump, since this came up with my playtest group.
Since I had to have something for the cleric to use, I came up with this on the spot:
You imbue yourself with holy power, exemplified by a glowing aura.
Effect: Fiends receive disadvantage on attacks they make against you, and you receive advantage on saves and checks versus spells or magical effects they use on you. This effect lasts until your concentration is broken, but for no longer than 1 minute.
You can choose to end the effect prematurely in order to try to banish a fiend. You touch the fiend and it must make a Wisdom save. If it fails, it is sent back to its home plane.