1 Kings 12:32-33

32And Jeroboam ordained a feast on the fifteenth day of the eighth month,1 like the feast that was in Judah, and he offered sacrifices on the altar; he made this offering in Bethel to sacrifice to the calves he had set up, and he installed priests in Bethel for the high places he had set up.

33On the fifteenth day of the eighth month, a month of his own choosing, Jeroboam offered sacrifices on the altar he had set up in Bethel. So he ordained a feast for the Israelites, offered sacrifices on the altar, and burned incense.