Arla's Dragonbane

Arla's Dragonbane is also known by the name of Sling +3. This is the most powerful sling available and a very powerful missile weapon. When this item is compared with standard slings, it offers a +3 bonus to speed, thaco and speed factor. Arla's Dragonbane can be found in the tower of Durlag at the fourth floor among the ornate graves, protected by many traps.

In-game description
"Sling +3: 'Arla's Dragonbane.' None know better the value of a well-placed when confronting a larger foe. This particular weapon was the property of a young woman named Arla Surestep, one of the few small-folk that leave the hearth to seek adventure. Legends speak of the diminutive Arla using the sling to place a well-sharpened pebble through the skull of a green dragon in mid-flight, though the same tales in another tavern places the stone squarely in the creature hindquarters for more humorous than lethal effects. It would seem that Halfings prefer entertainment over accuracy when it comes to their history."