Negative commandment · Lo Ta’aseh #15 of 613
Not to act as a missionary [madiach] to persuade the Jews to worship false gods]
שלא להדיח בני ישראל אחר עבודה זרה
The verse · Shemot 23:13
וּבְכֹל אֲשֶׁר־אָמַרְתִּי אֲלֵיכֶם תִּשָּׁמֵרוּ וְשֵׁם אֱלֹהִים אֲחֵרִים לֹא תַזְכִּירוּ לֹא יִשָּׁמַע עַל־פִּיךָ
“And all things that I have said to you be mindful of: and make no mention of the name of other gods, neither let it be heard out of thy mouth.”
The Rambam’s words
Not to act as a missionary [madiach] to persuade the Jews to worship false gods], as [Exodus 23:13] states: "And the name of other gods... shall not be heard from your mouth." [Our Sages taught that] this is a prohibition against acting as a missionary for the worship of false gods.
שלא להדיח בני ישראל אחר עבודה זרה, שנאמר "לא יישמע על פיך" (שמות כג,יג); זו אזהרה למדיח.
Why · Sefer HaChinuch #87
To not entice the Children of Israel towards idolatry
“The root of this commandment is well-known.”
Who & when
“And this prohibition is practiced in every place and at all times by males and females.”
Where in the Mishneh Torah
Hilchot Foreign Worship and Customs of the Nations הלכות עבודה זרה וחוקות הגויים