פירוש על דברי הימים א 1:33

And the sons of Midian: Ephah and Epher, etc. five heads of nations. Therefore, they appointed five kings, each one its king, as it is written (Num. 31:8): “Evi, and Rekem, and Zur, and Hur, etc., the five kings of Midian.”

all these were the sons of Keturah [These were mentioned] because of Abraham’s honor.