Light Crossbow +3

Light Crossbow +3 is an enchanted crossbow, which adds a -3 THACo and a +3 damage bonus to all bolts shot from it. It has a speed factor of 2 and it weighs 5 lbs. This item appears in Baldur's Gate II: Throne of Bhaal and Baldur's Gate II: Enhanced Edition.

It can be bought from the Tankard Tree and Karthis al-Hezzar

In-game description
"A crossbow is a bow mounted crosswise on a wooden or metal shaft, the latter called a tiller. The bow is usually made of ash or yew. The crossbow fires a quarrel (also called a bolt). This magical crossbow is elegant and light in the hand, with little recoil."