Fret not thyself because of evildoers. According to Aristotle, we have a special emotion implanted in our nature— νέμεσις—which causes us to "fret" when we witness undeserved prosperity ('Rhet.,' 2.9, § 1).
Certainly the feeling is very common and very strong; it is also characteristic of the best natures (see Psalms 73:3-14; Job 21:7-15; Jeremiah 12:1, Jeremiah 12:2; Malachi 3:15). The feeling does not need to be eradicated, but only to be held in check.
Faith in God's retributive justice will enable us calmly to await "the end" (Psalms 73:17), in full assurance that ultimately God's vengeance will overtake the wicked man, and he will receive condign punishment.
Neither be thou envious against the workers of iniquity. Envy is not a natural passion. To envy the evil-doers on account of their prosperity is at once a folly and a danger. Their position is really not enviable; and, if we allow ourselves to envy them, we shall be tempted to follow their example (see Proverbs 24:1).