When Yeshayah said, “for I am a man of impure lips and I dwell among an impure people” (Yeshayah 6:6), Hashem said to him, “Yeshayah, you are permitted to say “I am a man of impure lips” about yourself, but about Israel you say “And i dwell among an impure people?!”

The verse says “and one of the Seraphim came upon me and in his hand was a burning coal.”  What is meant by a burning coal?  A burning coal [to be thrown] on one who speaks lashon hara about my child. ~ Midrash Tanchuma, Vayishlach