Positive commandment · Mitzvat Aseh #219 of 613
For a person who made defamatory remarks about his wife to remain married to her for his entire life
לישב מוציא שם רע עם אשתו כל ימיו
The verse · Devarim 22:19
וְעָנְשׁוּ אֹתוֹ מֵאָה כֶסֶף וְנָתְנוּ לַאֲבִי הַנַּעֲרָה כִּי הוֹצִיא שֵׁם רָע עַל בְּתוּלַת יִשְׂרָאֵל וְלוֹ־תִהְיֶה לְאִשָּׁה לֹא־יוּכַל לְשַׁלְּחָהּ כׇּל־יָמָיו
“and they shall fine him a hundred shekels of silver, and give them to the father of the girl, because he has brought out an evil name upon a virgin of Yisra᾽el: and she shall be his wife; he may not put her away all his days.”
The Rambam’s words
For a person who made defamatory remarks about his wife to remain married to her for his entire life, as [Deuteronomy 22:19] states: "She shall become his wife. He may not send her away for his entire life."
לישב מוציא שם רע עם אשתו כל ימיו, שנאמר: "ולו תהיה לאישה" (דברים כב,יט).
Why · Sefer HaChinuch #553
The commandment that the wife of one who “puts out a bad name” about her dwell with him forever
“From the roots of the commandment [is that it is] to deter villains from engaging in such evil villainy, and like the matter that we will write adjacently below, with G-d’s help, about the law of rape (Sefer HaChinukh 557).”
Who & when
“And with regards to the lashes and the fine, it is practiced during the time of the Temple, when we were adjudicating the laws of fines.”
Where in the Mishneh Torah
Hilchot Virgin Maiden הלכות נערה בתולה