Negative commandment · Lo Ta’aseh #69 of 613
That one with a blemish not enter the entire sanctuary
שלא יכנס בעל מום מן המזבח ולפנים
The verse · Vayikra 21:23
אַךְ אֶל־הַפָּרֹכֶת לֹא יָבֹא וְאֶל־הַמִּזְבֵּחַ לֹא יִגַּשׁ כִּי־מוּם בּוֹ וְלֹא יְחַלֵּל אֶת־מִקְדָּשַׁי כִּי אֲנִי ה׳ מְקַדְּשָׁם
“Only he shall not go in unto the veil, nor come near to the altar, because he has a blemish; that he profane not my holy places: for I the Lord do sanctify them.”
The Rambam’s words
For a priest with a disqualifying physical deformity not to proceed beyond [the beginning of] the altar, as [Leviticus 21:23] states: "However, to the parochet he shall not approach."
שלא יכנס בעל מום מן המזבח ולפנים, שנאמר "אַךְ אֶל הַפָּרֹכֶת לֹא יָבֹא" (ויקרא כא, כג).
Why · Sefer HaChinuch #277
That one with a blemish not enter the entire sanctuary
“It is from the roots of the commandment to aggrandize the glory of the [Temple] and its beauty. Therefore it is not fitting for someone with a blemish to go there — since it is the place of perfection, it is not appropriate for someone with any lack to stand there.”
Where in the Mishneh Torah
Hilchot Admission into the Sanctuary הלכות ביאת מקדש