Leaven (Yeast): Leavened Bread Forbidden: At the Passover Meal
Source: Nav
Exodus 12:19, 20
For seven days there must be no leaven found in your houses. If anyone eats something leavened, that person, whether a foreigner or native of the land, must be cut off from the congregation of Israel. / You are not to eat anything leavened; eat unleavened bread in all your homes.”
Exodus 13:3, 4, 7
So Moses told the people, “Remember this day, the day you came out of Egypt, out of the house of slavery; for the LORD brought you out of it by the strength of His hand. And nothing leavened shall be eaten. / Today, in the month of Abib, you are leaving. / Unleavened bread shall be eaten during those seven days. Nothing leavened may be found among you, nor shall leaven be found anywhere within your borders.
Exodus 23:18
You must not offer the blood of My sacrifices with anything leavened, nor may the fat of My feast remain until morning.