Exodus 13:5-7

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

6“For seven days you must eat unleavened bread. The seventh day will be a pilgrimage festival in the Lord’s honor.

7Only unleavened bread should be eaten during these seven days. No sourdough or yeast should be seen anywhere in your territory.