Halakhah for Arakhin 32:10

That is that He commanded us to rebuke a sinner, or one who wants to sin, and to prevent him from it with words of rebuke. And it is not fitting to say, "Since I am not sinning, if someone besides me sins, what do I have to do with his God?" This is the opposite of the Torah. Rather we are commanded not to sin, and that we not let someone else of our faith rebel. And if he tries to rebel - and even if there is no testimony that has come out against him and judgement passed against him - we are obligated to rebuke him and bring him back. And that is His, may He be exalted, saying, "you shall surely rebuke your kinsman" (Leviticus 19:17). And included in this command is that some of us rebuke others of us when one man sins to another man, such that we not bear a grudge in our heart and we not think iniquitously about him. Rather, we are commanded to rebuke him with words until no [enmity] remains in the soul. And the language of the Sifra (Sifra, Kedoshim, Chapter 4:8) is, "From where [do we know] that if he reproved him [four or five] times, he should keep on reproving him? [Hence] we learn to say, 'you shall surely rebuke.' I might think that he must rebuke him [even if] his face changes color (in shame); [hence] we learn to say, 'but do not bear sin because of him.'" And the sages already explained that the obligation of this commandment is upon every man; and even the lesser one is obligated to rebuke the honored one. And even if he curses him and disgraces him, he must not turn away from rebuking him, until he [reaches the limit] - as the receivers of the Torah explained and said (Arakhin 16b) - "until [he] strikes [him]." And this commandment has stipulations and regulations that have been explained in scattered places in the Talmud. (See Parashat Kedoshim; Mishneh Torah, Human Dispositions 6.)