Exodus 13:5-7

13:5 When the Lord brings you to the land of the Canaanites, Hittites, Amorites, Hivites, and Jebusites, which he swore to your fathers to give you, a land flowing with milk and honey, then you will keep this ceremony in this month. 13:6 For seven days you must eat bread made without yeast, and on the seventh day there is to be a festival to the Lord. 13:7 Bread made without yeast must be eaten for seven days; no bread made with yeast shall be seen among you, and you must have no yeast among you within any of your borders.