Deuteronomy 16:3

3You shall not eat 16:3 Because yeast ferments and spreads throughout the dough, it was used symbolically to represent the spread of sin.leavened bread with it; instead, for seven days you shall eat the Passover with unleavened bread, the bread of affliction (for you left the land of Egypt in haste); [do this] so that all the days of your life you may remember [thoughtfully] the day when you came out of the land of Egypt.