Negative commandment · Lo Ta’aseh #356 of 613
That he not bring back his ex-wife from when she has married
שלא יחזיר המגרש גרושתו אחר שנישאת לאחר
The verse · Devarim 24:4
לֹא־יוּכַל בַּעְלָהּ הָרִאשׁוֹן אֲשֶׁר־שִׁלְּחָהּ לָשׁוּב לְקַחְתָּהּ לִהְיוֹת לוֹ לְאִשָּׁה אַחֲרֵי אֲשֶׁר הֻטַּמָּאָה כִּי־תוֹעֵבָה הִוא לִפְנֵי ה׳ וְלֹא תַחֲטִיא אֶת־הָאָרֶץ אֲשֶׁר ה׳ אֱלֹהֶיךָ נֹתֵן לְךָ נַחֲלָה
“then her former husband, who sent her away, may not take her again to be his wife, after she is defiled; for that is abomination before the Lord: and thou shalt not cause the land to be sinful, which the Lord thy God gives thee for an inheritance.”
The Rambam’s words
For a man who is divorced not to remarry his divorcee after she marries anyone else, as [Deuteronomy 24:4] states: "Her first husband who divorced her may not take her as a wife again."
שלא יחזיר המגרש גרושתו אחר שנישאת לאחר, שנאמר "לא יוכל בעלה הראשון אשר שילחה לשוב לקחתה" (דברים כד,ד).
Who & when
“And this prohibition is practiced in every place and at all times by males — as the warning to not bring them back comes to them.”
Where in the Mishneh Torah
Hilchot Divorce הלכות גירושין