Negative commandment · Lo Ta’aseh #359 of 613
For a person who defamed his wife's character not to divorce her
שלא יגרש מוציא שם רע את אשתו
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 defamed his wife's character not to divorce her, as [Deuteronomy 22:19] states: "He may not send her away for his entire life."
שלא יגרש מוציא שם רע את אשתו, שנאמר בו "לא יוכל לשלחה כל ימיו" (דברים כב,יט).
Why · Sefer HaChinuch #554
That he should not divorce her all of his days
“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).”
Where in the Mishneh Torah
Hilchot Virgin Maiden הלכות נערה בתולה