Talk to Zealot Ware (one of the bald guy with armor and weapon) and he'll talk about convincing Brother Devin to quit his fasting. If you agree to talk him out of it, this quest will start. Talk to Devin and convince him you're Atom's messenger to make him stop. (perform the quicksave-reload method even if the speech check is red) Once done, talk to Ware to complete the quest. You'll also receive Ware's Brew and the recipe to make it.