Hilchot Tshuva, Chapter 1, Halacha 4

Moving right along, Rambam continues with the concept that the essence of Tshuva is “Confession”, and atonement for sin can only be granted if you verbalise the nature of the sin. He also introduces the concept of abandoning the sin. Interesting to note that he didn’t start off with the concept of abandoning the sin before beginning the Tshuva process (compare to Sharei Tshuva)

הִלְכּוֹת תְּשׁוּבָה פֵּרֶק א, הלכה ד

וְכֵן כָּל מְחֻיְּבֵי מִיתוֹת בֵּית דִּין, וּמְחֻיְּבֵי מַלְקוּת--אֵין מִתְכַּפֵּר לָהֶם בְּמִיתָתָם אוֹ בִּלְקִיָּתָם, עַד שֶׁיַּעֲשׂוּ תְּשׁוּבָה וְיִתְוַדּוּ. וְכֵן הַחוֹבֵל בַּחֲבֵרוֹ אוֹ הַמַּזִּיק מָמוֹנוֹ--אַף עַל פִּי שֶׁשִּׁלַּם לוֹ מַה שְׁהוּא חַיָּב לוֹ--אֵין מִתְכַּפֵּר לוֹ, עַד שֶׁיִּתְוַדֶּה וְיָשׁוּב מִלַּעֲשׂוֹת כְּזֶה לְעוֹלָם: שֶׁנֶּאֱמָר "מִכָּל-חַטֹּאת הָאָדָם" (במדבר ה,ו).

Hilchot Tshuva, Chapter 1, Halacha 4

And similarly, anyone who deserves death from a Beit Din, or deserves lashes – the lashes or death do not grant atonement, unless he did tshuva and confessed. Similarly, if one injured his fellow or caused him financial damage – even though he paid him what he owes him, he does not not receive atonement unless he confesses, and accepts not to do the action again, ever, as it is written: “From every sin of man” (Bamidbar 5:6).