The Bowstring of Gond is an item found in Sendai's Enclave. This item appears in Baldur's Gate II: Throne of Bhaal. Cespenar can use this item to upgrade the Darkfire Bow, Firetooth or Taralash.
It can be gained from the Captain Egeissag who you will most likely be facing in a one-on-one pit fight.
|“||Gond Wonderbringer, the God of invention and innovation, created this enchanted bowstring to improve the accuracy of even the most powerful of magical bows.||”|