Jeroboam also instituted a religious festival on the fifteenth day of the eighth month, like the festival in Judah. On the altar in Bethel he offered sacrifices to the gold bull-calves he had made, and he placed there in Bethel the priests serving at the places of worship he had built. 1
References for 1 Kings 12:32
12.32, 33 Lv 23.33, 34.