SRD:Merciful

Merciful: The weapon deals an extra 1d6 points of damage, and all damage it deals is nonlethal damage. On command, the weapon suppresses this ability until commanded to resume it. Bows, crossbows, and slings so crafted bestow the merciful effect upon their ammunition.

Faint conjuration; CL 5th; Craft Magical Arms and Armor, cure light wounds; Price +1 bonus.