הלכה על אבות 3:15

To not whiten the face of an Israelite: To not embarrass an Israelite; and our Rabbis, may their memory be blessed, called this sin (Avot 3:15), "whitening the face of his fellow in public. And the negative commandment that comes about this [in the Torah] is that which is written (Leviticus 19:17), "you shall surely rebuke your compatriot, and you shall not bear a sin for him." And they said in Sifra, Kedoshim 4:8, "From where [do we know] that if you rebuked him four or five times [...] go back and rebuke [him again]? [Hence] we learn to say, 'you shall surely rebuke.' Perhaps, he should rebuke and his face change [color]? [Hence] we learn to say, 'and you shall not bear a sin for him.'"