Positive commandment · Mitzvat Aseh #61 of 613
For all animal offerings to be unblemished
להיות כל קרבן בהמה תמים
The verse · Vayikra 22:21
וְאִישׁ כִּי־יַקְרִיב זֶבַח־שְׁלָמִים לַה׳ לְפַלֵּא־נֶדֶר אוֹ לִנְדָבָה בַּבָּקָר אוֹ בַצֹּאן תָּמִים יִהְיֶה לְרָצוֹן כׇּל־מוּם לֹא יִהְיֶה־בּוֹ
“And whoever offers a sacrifice of peace offerings to the Lord to accomplish his vow, or a freewill offering in oxen or sheep, it shall be perfect to be accepted; no blemish shall be in it.”
The Rambam’s words
For all animal offerings to be unblemished, as [Leviticus 22:21] states: "[When it is] unblemished, it will be desirable...."
להיות כל קרבן בהמה תמים, שנאמר: "תָּמִים יִהְיֶה לְרָצוֹן" (ויקרא כב, כא).
Why · Sefer HaChinuch #286
Sacrifice being unblemished
“The root of the commandment is revealed with that which we [wrote] previously above regarding sacrifices from the angle of the simple understanding, [which is] that they are to arouse and direct the thoughts of people towards G-d, blessed be He.”
Who & when
“And this commandment is practiced at the time of the [Temple].”
Where in the Mishneh Torah
Hilchot Things Forbidden on the Altar הלכות איסורי המזבח