Exodus 12:18-20

18In the first month, on the fourteenth day of the month at even, ye shall eat unleavened bread, until the one and twentieth day of the month at even. 19Seven days shall there be no leaven found in your houses: for whosoever eateth that which is leavened, even that soul shall be cut off from the congregation of Israel, whether he be a stranger, or born in the land. 20Ye shall eat nothing leavened; in all your habitations shall ye eat unleavened bread.