Exodus 23:14-17

MKJV(i) 14 You shall keep a feast to Me three times in the year. 15 You shall keep the Feast of Unleavened Bread. You shall eat unleavened bread seven days, as I commanded you, in the time appointed of the month Abib, for in it you came out of Egypt. And no one shall appear before Me empty. 16 Also the Feast of Harvest, the first-fruits of your labors, which you have sown in the field. Also the Feast of Ingathering, in the end of the year, when you have gathered in your labors out of the field. 17 Three times in the year all your males shall appear before the Lord God.
Reformed Dating