Hammer Blow

 
Prerequisite(s): Base Attack Bonus 6+ Power Attack, Flurry of Blows ability.
 
Benefit: In lieu of an extra attack when using Flurry of Blows, you add damage top your first attack equal to the base attack bonus of the sacrificed extra attack, minus the Flurry of Blows penalty.
 
Source: Mongoose Ultimate Feats