Negative commandment · Lo Ta’aseh #314 of 613
Not to diminish from any of the mitzvot of the Torah
שלא לגרוע מכל מצוות התורה
The verse · Devarim 13:1
אֵת כׇּל־הַדָּבָר אֲשֶׁר אָנֹכִי מְצַוֶּה אֶתְכֶם אֹתוֹ תִשְׁמְרוּ לַעֲשׂוֹת לֹא־תֹסֵף עָלָיו וְלֹא תִגְרַע מִמֶּנּוּ
“Every matter which I command you, observe to do it: thou shalt not add thereto, nor diminish from it.”
The Rambam’s words
Not to diminish from any of the mitzvot of the Torah, as [Deuteronomy, ibid.] continues: "...and do not diminish from it."
שלא לגרוע מכל מצוות התורה, שנאמר "ולא תגרע ממנו" (דברים יג,א).
Why · Sefer HaChinuch #455
To not subtract from the commandments of the Torah
“From the roots of the commandment is like the matter that we said in the commandment of “do not add,” that preceded it. And the rest of all of its matters are like it [as well].”
Where in the Mishneh Torah
Hilchot Rebels הלכות ממרים