Who prophesied to Jehoshaphat, "The battle does not belong to you, but to God"?

Answer: Jahaziel

The Spirit of the LORD came on Jahaziel, a Levite descended from Asaph, who told Judah not to fear the vast army.

“Then the Spirit of the LORD came upon Jahaziel son of Zechariah, the son of Benaiah, the son of Jeiel, the son of Mattaniah, a Levite from Asaph’s descendants, as he stood in the midst of the assembly.”— 2 Chronicles 20:14 (BSB)