On 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.
Jewish Publication Society of America Version (JPS1917) - 1 Kings 12:33 >And he went up unto the altar which he had made in Beth-el on the fifteenth day in the eighth month, even in the month which he had devised of his own heart; and he ordained a feast for the children of Israel, and went up unto the altar, to offer.