Who told King Asa, "If you seek Him, He will be found by you"?

Answer: Azariah son of Oded

The Spirit of God came on Azariah son of Oded, who told Asa the LORD is with those who are with Him.

“Now the Spirit of God came upon Azariah son of Oded. So he went out to meet Asa and said to him, “Listen to me, Asa and all Judah and Benjamin. The LORD is with you when you are with Him. If you seek Him, He will be found by you, but if you forsake Him, He will forsake you.”— 2 Chronicles 15:1-2 (BSB)