A 9-year-old boy fired a pistol near Fordham University after he found the weapon in the lobby of a building, police sources said.

The young boy spotted the gun in the lobby on Marion Avenue near East 195th Street on Saturday and picked it up, sources said.

It wasn’t immediately clear if he lived there or who he was with, cops said.

He fired the .22-caliber gun once and struck a wall, but nobody was injured, cops said.

Investigators are still trying to determine who placed the firearm there