Negative commandment · Lo Ta’aseh #118 of 613
Not to allow the meat of the Chaggigah sacrifice to remain until the third day
שלא להותיר מחגיגת ארבעה עשר ליום השלישי
The verse · Devarim 16:4
וְלֹא־יֵרָאֶה לְךָ שְׂאֹר בְּכׇל־גְּבֻלְךָ שִׁבְעַת יָמִים וְלֹא־יָלִין מִן־הַבָּשָׂר אֲשֶׁר תִּזְבַּח בָּעֶרֶב בַּיּוֹם הָרִאשׁוֹן לַבֹּקֶר
“And there shall be no leaven seen with thee in all thy border for seven days; nor shall any thing of the meat, which thou dost sacrifice on the first day at evening, remain all night until the morning.”
The Rambam’s words
Not to allow the meat of the Chaggigah sacrifice to remain until the third day, as [Deuteronomy 16:4] states: "Do not leave over any of the meat...." According to the oral tradition, we have learned that the verse refers to the Chaggigah sacrifice offered on the fourteenth of Nisan. The phrase "until the morning" [in that verse] refers to the morning of the second day of Pesach, the third day after [the sacrifice] was offered.
שלא להותיר מחגיגת ארבעה עשר ליום השלישי, שנאמר "ולא ילין מן הבשר" (דברים טז,ד); מפי השמועה למדו שבבשר חגיגת ארבעה עשר הכתוב מדבר, וזה שנאמר "לבוקר" (שם) לבוקרו של יום שני של פסח, שהוא שלישי לשחיטה.
Why · Sefer HaChinuch #486
To not leave over from the festive (chagigah) sacrifice to the third day
“From the roots of the commandment is the fixed foundation that we have about the commandment of the matter of the Pesach [sacrifice], which is a strong commandment and foundation in our Torah.”
Who & when
“And this commandment is practiced at the time of the [Temple] by males and females; as even women are obligated in peace-offerings of joy — even though [they are] caused by time — just as they are obligated in resting on [the festival of which it is a part].”
Where in the Mishneh Torah
Hilchot Paschal Offering הלכות קרבן פסח