לֹא־תֹאכַ֤ל עָלָיו֙ חָמֵ֔ץ שִׁבְעַ֥ת יָמִ֛ים תֹּֽאכַל־עָלָ֥יו מַצּ֖וֹת לֶ֣חֶם עֹ֑נִי כִּ֣י בְחִפָּז֗וֹן יָצָ֙אתָ֙ מֵאֶ֣רֶץ מִצְרַ֔יִם לְמַ֣עַן תִּזְכֹּר֔ אֶת־י֤וֹם צֵֽאתְךָ֙ מֵאֶ֣רֶץ מִצְרַ֔יִם כֹּ֖ל יְמֵ֥י חַיֶּֽיךָ׃
Thou shalt eat no leavened bread with it; seven days shalt thou eat unleavened bread therewith, even the bread of affliction; for in haste didst thou come forth out of the land of Egypt; that thou mayest remember the day when thou camest forth out of the land of Egypt all the days of thy life.
Shenei Luchot HaBerit
Commandment 485 forbids consumption of leavened products as of noon on the fourteenth of Nissan. The Torah (16,3) writes: "You shall not eat the Passover while anything leavened may be eaten." This refers to the time when the Passover lamb may already be slaughtered.