Exodus 12:17-20

17And ye shall keep the [feast of] unleavened [bread]; for in this same day have I brought your hosts out of the land of Egypt; and ye shall keep this day in your generations [as] an ordinance for ever.

18In the first [month], on the fourteenth day of the month, in the evening, ye shall eat unleavened bread until the one and twentieth day of the month in the evening.

19Seven days shall there be no leaven found in your houses; for whoever eateth what is leavened — that soul shall be cut off from the assembly of Israel, whether he be a sojourner, or born in the land.

20Ye shall eat nothing leavened: in all your dwellings shall ye eat unleavened bread.