(Devarim 16:4) "And there shall not be seen unto you leaven in all of your border for seven days": "yours" you may not see, but you may see that of others (gentiles) and that of the Temple (i.e., if there were chametz of the Temple in his house, he is not in transgression of "there shall not be seen unto you.")
"shall not be seen unto you": Do not see it as being yours, but void it in your heart — whence they ruled: "If one were on his way (on the fourteenth of Nissan) to slaughter his Pesach offering, or to circumcise his son, or to eat the betrothal feast in the house of his father-in-law, and he remembered that he had chametz in his house — if he can return (home) and burn it and return to his mitzvah, he should do so; if not, he should void it in his heart.
"and there shall not be seen unto you leaven": This is the difference between Beth Hillel and Beth Shammai: Beth Shammai say: Leaven (is forbidden) in (the size of) an olive, and chametz in (the size of) a date (less than an olive). Beth Hillel say: Both in (the size of) an olive.
"and there shall not remain of the flesh that you sacrifice in the evening on the first day until the morning": Which offering do you sacrifice in order to eat it in the evening? This is the chagigah (the festive offering), which is eaten together with the Pesach.
(דברים טז ד) לֹא יֵרָאֶה לְךָ שְׂאֹר, רוֹאֶה אַתָּה לַאֲחֵרִים; לֹא יֵרָאֶה לְךָ שְׂאֹר, רוֹאֶה אַתָּה לַגָּבוֹהַּ; לֹא יֵרָאֶה לְךָ שְׂאֹר, רוֹאֶה אַתָּה בַּפְּלַטְיָא.
(Devarim 16:4) "And there shall not be seen unto you leaven in all of your border for seven days": "yours" you may not see, but you may see that of others (gentiles) and that of the Temple (i.e., if there were chametz of the Temple in his house, he is not in transgression of "there shall not be seen unto you.")
לֹא יֵרָאֶה לְךָ שְׂאֹר, בַּטֵּל בְּלִבְּךָ! מִכָּאן אָמְרוּ (פסחים ג ז): הַהוֹלֵךְ לִשְׁחוֹט אֶת פִּסְחוֹ וְלָמוּל אֶת בְּנוֹ, וְנִזְכַּר שֶׁיֵּשׁ לוֹ חָמֵץ בְּתוֹךְ בֵּיתוֹ – אִם יָכוֹל לַחֲזוֹר וּלְבַעֵר וְלַחֲזוֹר לְמִצְוָתוֹ – יַחֲזוֹר; וְאִם לָאו – יְבַטֵּל בְּלִבּוֹ.
"shall not be seen unto you": Do not see it as being yours, but void it in your heart — whence they ruled: "If one were on his way (on the fourteenth of Nissan) to slaughter his Pesach offering, or to circumcise his son, or to eat the betrothal feast in the house of his father-in-law, and he remembered that he had chametz in his house — if he can return (home) and burn it and return to his mitzvah, he should do so; if not, he should void it in his heart.
(שמות יג ז) ״לֹא יֵרָאֶה לְךָ חָמֵץ וְלֹא יֵרָאֶה לְךָ שְׂאֹר״ – זֶהוּ חִלּוּק שֶׁבֵּין בֵּית שַׁמַּיי לְבֵית הִלֵּל (ביצה פ״א מ״א) שֶׁבֵּית שַׁמַּיי אוֹמְרִים: שְׂאוֹר כַּזַּיִת וְחָמֵץ כַּכּוֹתֶבֶת, וּבֵית הִלֵּל אוֹמְרִים: זֶה וָזֶה כַּזַּיִת.
"and there shall not be seen unto you leaven": This is the difference between Beth Hillel and Beth Shammai: Beth Shammai say: Leaven (is forbidden) in (the size of) an olive, and chametz in (the size of) a date (less than an olive). Beth Hillel say: Both in (the size of) an olive.
וְלֹא יָלִין מִן הַבָּשָׂר אֲשֶׁר תִּזְבַּח בָּעֶרֶב, אֵיזוֹ זְבִיחָה אַתָּה זוֹבֵחַ עַל מְנָת לֶאֱכוֹל לָעֶרֶב? הֱוֵי אוֹמֵר זֶה הַפֶּסַח.
"and there shall not remain of the flesh that you sacrifice in the evening on the first day until the morning": Which offering do you sacrifice in order to eat it in the evening? This is the chagigah (the festive offering), which is eaten together with the Pesach.
בַּיּוֹם הָרִאשׁוֹן לַבֹּקֶר, לְבָקְרוֹ שֶׁל שְׁלִישִׁי אוֹ יָכוֹל לְבָקְרוֹ שֶׁל שֵׁנִי? תַּלְמוּד לוֹמַר: ״נֶדֶר״, (ויקרא ז טז) ״אִם נֶדֶר״; ״נְדָבָה״, (ויקרא ז טז) ״אוֹ נְדָבָה״, לְרַבּוֹת חֲגִיגָה הַבָּאָה עִם הַפֶּסַח, שֶׁתֵּאָכֵל לִשְׁנֵי יָמִים. הָא מָה אֲנִי מְקַיֵּם לַבֹּקֶר? לְבָקְרוֹ שֶׁל שְׁלִישִׁי.
"in the first day until the morning": the morning of the second day.