You have mastered the style of fighting with hammer and axe at the same time, and have learned to deal thunderous blows with this unique pairing of weapons.
Prerequisites: Str 13, Improved Sunder, Power Attack, Two-Weapon Fighting, Weapon Focus (warhammer or light hammer), Weapon Focus (battleaxe, handaxe, or dwarven waraxe).
Benefit: If you hit the same creature with both your axe and your hammer in the same round, it must make a Fortitude saving throw (DC 10 + ½ your character level + your Str modifier) or be dazed for 1 round.
Source: Complete Warrior, page 112.