Exodus 13:5-7

5When the Lord brings you into the land of the Canaanites, Hethites, Amorites, Hivites, and Jebusites, which he swore to your ancestors that he would give you, a land flowing with milk and honey, you must carry out this ceremony in this month.

6For seven days you must eat unleavened bread, and on the seventh day there is to be a festival to the Lord.

7Unleavened bread is to be eaten for those seven days. Nothing leavened may be found among you, and no yeast may be found among you in all your territory.