Exodus 13:5-7

5And when the LORD brings you into the land of the Canaanites, Hittites, Amorites, Hivites, and Jebusites—the land He swore to your fathers that He would give you, a land flowing with milk and honey—you shall keep this service in this month.

6For seven days you are to eat unleavened bread, and on the seventh day there shall be a feast to the LORD. 7Unleavened bread shall be eaten during those seven days. Nothing leavened may be found among you, nor shall leaven be found anywhere within your borders.