Gong Mallet

Gong Mallet is an quest item needed in Baldur's Gate and Baldur's Gate: Enhanced Edition.It's made by  combining the mallet head and the mallet handle at the anvil, which in the northwest in this area. The mallet head can be found in the area with the books. The mallet handle can be found in a container near the four guardians of the entrance to the second undergound level.

In-game description
"This appears to be a mallet for a gong of some kind."