Who first said Naaman could be cured by the prophet in Samaria?

Answer: A captive Israelite girl

A young girl taken from Israel, who served Naaman's wife, said the prophet in Samaria could cure his leprosy.

“At this time the Arameans had gone out in bands and had taken a young girl from the land of Israel, and she was serving Naaman’s wife. She said to her mistress, “If only my master would go to the prophet who is in Samaria, he would cure him of his leprosy.””— 2 Kings 5:2-3 (BSB)