Mishneh Torah — Positive Mitzvot מצוות עשה, Chapter 60
The full Hebrew text of Mishneh Torah, Positive Mitzvot, Chapter 60, with English translation by Maimonides (Rambam).
להיות כל קרבנות בהמה מיום שמיני והלאה, שנאמר: "מִיּוֹם הַשְּׁמִינִי וָהָלְאָה" (ויקרא כב, כז).
For all animals to be sacrificed after their eighth day [of life], as [Leviticus 22:27] states: "And on the eighth day and afterwards...."