Albert Barnes Commentary 2 Chronicles 20:34

"Now the rest of the acts of Jehoshaphat, first and last, behold, they are written in the history of Jehu the son of Hanani, which is inserted in the book of the kings of Israel." — 2 Chronicles 20:34 (ASV)

Who is mentioned ... - Words which are now generally thought to mean “whose work was inserted into the Book of the Kings.”

Of Israel - “Israel” is probably used here inexactly for “Judah” (compare 2 Chronicles 12:6; 2 Chronicles 21:2; 2 Chronicles 21:4).