Rambam in Hilchot De'ot gives laws of who, what, where, when, and how to rebuke according to Halacha. Rabbi Yaron Reuven reviews the obligation to rebuke, when you should, when you shouldn't, and when you have to in order to avoid having their sins go to your account. The Rambam brings the Sages in Masechet Sanhedrin 93B that say one that doesn't rebuke is not given the opportunity to do TeShuva.