Albert Barnes Commentary 2 Kings 25:25-26

"But it came to pass in the seventh month, that Ishmael the son of Nethaniah, the son of Elishama, of the seed royal, came, and ten men with him, and smote Gedaliah, so that he died, and the Jews and the Chaldeans that were with him at Mizpah. And all the people, both small and great, and the captains of the forces, arose, and came to Egypt; for they were afraid of the Chaldeans." — 2 Kings 25:25-26 (ASV)

Jeremiah gives this history in great detail (Jeremiah 41–43).