Mishneh Torah — Positive Mitzvot מצוות עשה, Chapter 43
The full Hebrew text of Mishneh Torah, Positive Mitzvot, Chapter 43, with English translation by Maimonides (Rambam).
להוסיף קרבן בחג הפסח, שנאמר: "שִׁבְעַת יָמִים תַּקְרִיבוּ אִשֶּׁה לַיי" (ויקרא כג, לו).
To offer an additional sacrifice on Pesach, as [Leviticus 23:36] states: "For seven days, you will bring a fire offering unto God...."