Exodus 23:15-18

15You are to observe the Feast of Unleavened Bread; seven days you must eat bread made without yeast, as I commanded you, at the appointed time of the month of Abib, for at that time you came out of Egypt. No one may appear before me empty-handed.

16“You are also to observe the Feast of Harvest, the firstfruits of your labors that you have sown in the field, and the Feast of Ingathering at the end of the year when you have gathered in your harvest out of the field.

17At three times in the year all your males will appear before the Lord God.

18“You must not offer the blood of my sacrifice with bread containing yeast; the fat of my festal sacrifice must not remain until morning.