Musar על בבא קמא 184:13

The righteous people reject the wicked, and our Sages, of blessed memory said, "Not for nothing did the starling follow the raven, but because it is of the same kind" (Baba Kamma 92b). And it is said, "Every fowl dwells near its kind and man near his equal" (Ben Sira 13:5). And they said, "It is forbidden to look at the form of a wicked man" (Megillah 28a), as it is said, "Were it not that I regard the presence of Jehoshaphat the king of Judah, I would not look toward thee, nor see thee" (II Kings 3:14). And everyone who looks at the form of a wicked man, his eyes grow dim in his old age, like Isaac, our father, whose eyes grew dim because he looked upon Esau, even though he did not know of Esau's evil deeds.