Mishneh Torah — Negative Mitzvot מצוות לא תעשה, Chapter 116
The full Hebrew text of Mishneh Torah, Negative Mitzvot, Chapter 116, with English translation by Maimonides (Rambam).
שלא להניח אימורי הפסח עד שיפסלו בלינה, שנאמר "ולא ילין חלב חגי, עד בוקר" (שמות כג,יח).
Not to allow the sacrificial portions of the Paschal sacrifice to become disqualified by remaining overnight, as [Exodus 23:18] states: "Do not allow the fat of My festive offering to remain until the morning."