Leaven: Forbidden: During the Feast of the Passover
Source: TTT
Exodus 12:15–20
For seven days you must eat unleavened bread. On the first day you are to remove the leaven from your houses. Whoever eats anything leavened from the first day through the seventh must be cut off from Israel. / On the first day you are to hold a sacred assembly, and another on the seventh day. You must not do any work on those days, except to prepare the meals—that is all you may do. / So you are to keep the Feast of Unleavened Bread, for on this very day I brought your divisions out of the land of Egypt. You must keep this day as a permanent statute for the generations to come.