Exodus 12:18-21

The bread you eat must be made without yeast from the evening of the fourteenth day of the first month until the evening of the twenty-first day of that month. During those seven days, there must be no trace of yeast in your homes. Anyone who eats anything made with yeast during this week will be cut off from the community of Israel. These regulations apply both to the foreigners living among you and to the native-born Israelites. During those days you must not eat anything made with yeast. Wherever you live, eat only bread made without yeast.” Then Moses called all the elders of Israel together and said to them, “Go, pick out a lamb or young goat for each of your families, and slaughter the Passover animal.