Mishneh Torah — Positive Mitzvot מצוות עשה, Chapter 73

להתוודות לפני ה' מכל חטא שיעשה האדם, בשעת הקרבן ושלא בשעת הקרבן, שנאמר: "והתוודו, את חטאתם אשר עשו" (במדבר ה,ז).

For a person to confess before God for any sin which he has committed. [This applies] when he brings a sacrifice [for atonement] and when he does not bring a sacrifice, as [Numbers 5:6] states: "And they shall confess the sins that they committed." the Rambam defines this mitzvah as return to God and repentance, a more encompassing service, of which confession is only one facet.(See Hilchot Teshuvah 2:2.)