Thunderstone (3.5e Monk Fighting Style)
From D&D Wiki
The path of the thunderstone uses the sling as its signature weapon. This style is especially popular with halflings.
1st-Level Skill Bonus
Point Blank Shot
Shot on the Run
6th-Level Bonus Ability
Once per day per monk level, treat one attack with an ordinary stone as if using a thunderstone. This is an extraordinary ability. The DC against the deafening effect is 10 + half your monk level + Wis bonus.
Prerequisites: Concentration 8 ranks, Weapon Focus (sling)