Musar zu Mischlej 29:26

But in honoring the wicked there is a profanation of the Torah and of God's service, and this is a transgression that wears away flesh and bone. Then again, many may be drawn to do similarly and they receive retribution, and in this vein the Sages said, "Woe to the wicked, woe to his neighbour" (Nega'im 2:6). Moreover, in honoring the wicked the honor of the righteous is brought low, and there is no honor to the righteous except after the degradation of the wicked. And since there is a stumbling block to the world in the honoring of the wicked one should guard himself against speaking good of the wicked, nor should one mention them for good, as it is said, "But the name of the wicked shall rot" (Prov. 10:7). And it is written, "An unjust man is an abomination to the righteous" (Prov. 29:26). And if a man does not want to speak of the wickedness of a wicked man let him not speak of his goodness.