The Prohibitionist

 is a mission in Red Dead Redemption.

Story
A preacher man (Abner) is preaching from his bible outside your hotel in Blackwater, upon talking to him, he tells you how the townsfolk aren't too fond of him. He proves it to you by sending you to one of his disgruntled listeners.

Walkthrough
The listener orders you to kill Abner. But you have the choice to either kill or warn Abner. After doing either you return to the listener. If you warn Abner, you are rewarded with a small amount of money ($23) and, upon returning to the bartender, +5 fame. However, the bartender says that he will charge you double at his bar because of that. If you kill Abner, you lose 20 points of honor, gain a $20 bounty, and when you return to the bartender he rewards you with $26.