An idol
So Sennacherib king of Assyria departed, and went and returned, and dwelt at Nineveh. And it came to pass, as he was worshipping in the house of Nisroch his god, that Adrammelech and Sharezer his sons smote him with the sword: and they escaped into the land of Armenia. And Esar-haddon his son reigned in his stead. (2 Kings 19:36-37)
So Sennacherib king of Assyria departed, and went and returned, and dwelt at Nineveh. And it came to pass, as he was worshipping in the house of Nisroch his god, that Adrammelech and Sharezer his sons smote him with the sword; and they escaped into the land of Armenia: and Esar-haddon his son reigned in his stead. (Isaiah 37:37-38)