1 Kings 12:31-32

31He also made shrines on the high places and appointed priests from among the people, who were not sons of Levi.

32Then Jeroboam instituted a festival in the eighth month, on the fifteenth day of the month, imitating the Festival that is in Judah. He went up to the altar that he built in Bethel, to sacrifice to the calves that he had made. He installed in Bethel the priests of the high places that he made.