"Whoever rebukes his fellow man, whether concerning matters between the two of them or between him [the fellow man] and God, needs to rebuke him in p… - Moshe ben Maimon

"Whoever rebukes his fellow man, whether concerning matters between the two of them or between him [the fellow man] and God, needs to rebuke him in private. He shall speak to him calmly and gently, and make known to him that he talks to him only for his own good, to bring him to the life of the world-to-come. If he accepts it from him, good; if not, he shall rebuke him a second and a third time. Thus he is always obliged to rebuke him until the sinner strikes him and says to him, "I will not listen." If he does not prevent everything he can possibly prevent, he is ensnared in the sin of all those he could have prevented from sinning."