Negative commandment · Lo Ta’aseh #96 of 613
Not to offer an animal with a disqualifying physical blemish as a sacrifice when it was brought by gentiles
שלא להקריב בעל מום מיד הגויים
The verse · Vayikra 22:25
וּמִיַּד בֶּן־נֵכָר לֹא תַקְרִיבוּ אֶת־לֶחֶם אֱלֹהֵיכֶם מִכׇּל־אֵלֶּה כִּי מׇשְׁחָתָם בָּהֶם מוּם בָּם לֹא יֵרָצוּ לָכֶם
“Neither from a stranger’s hand shall you offer the bread of your God from any of these; because their corruption is in them, their blemish is in them: they shall not be accepted for you.”
The Rambam’s words
Not to offer an animal with a disqualifying physical blemish as a sacrifice when it was brought by gentiles, as [Leviticus 22:25] states: "Do not offer sacrifices [from these animals] when they are given by gentiles."
שלא להקריב בעל מום מיד הגויים, שנאמר "ומיד בן נכר, לא תקריבו" (ויקרא כב,כה).
Why · Sefer HaChinuch #292
Not to sacrifice a sacrifice that is one with a blemish from the hand of the stranger
“It is from the roots of the commandment [that it is] since there would be a disgrace to the consecrated animals with this. And I have already written many times (Sefer HaChinukh 95) [about] the benefit to the heart of man that comes out [from] the endearment of the glory of the Temple, its servants and its offerings.”
Who & when
“And [it] is practiced by the priests at the time that Israel is dwelling on its land, because then is the time of offering.”
Where in the Mishneh Torah
Hilchot Things Forbidden on the Altar הלכות איסורי המזבח