Fret not thyself because of evildoers, neither be thou envious against the workers of iniquity....Rest in the LORD, and wait patiently for him: fret not thyself because of him who prospereth in his way, because of the man who bringeth wicked devices to pass. Cease from anger, and forsake wrath: fret not thyself in any wise to do evil. (Ps. 37.1, 7-8)
Fret not thyself because of evil men, neither be thou envious at the wicked: (Prov. 24.19)
Eric Liddell: Jennie, Jennie, don't fret yourself. (Chariots of Fire)
Obadiah Sedgwick, Providence Handled Practically, p. 39:
If there is a providence that generally extends to all, and especially to the people of God, then we should learn not to vex and disquiet our minds and hearts. This is what Christ taught His disciples: since there was a God who looked to the grass and to the lilies, and a Father who cared for them, therefore they should not take thought and worry (Matt. 6:28), and their hearts should not be troubled. 1 Peter 5:7 advises you to live "casting all your care upon him; for he careth for you." By this, Peter means that you must not perplex yourselves about your conditions, your safeties, or your supports. You may ease yourselves of all this worry, for there is a God who takes care of you, who minds you, who thinks on you, who will provide well enough for you. Philippians 4:5 advises, "Let your moderation be known unto all men. The Lord is at hand." Do not rend yourselves with excessive grief, vastness of getting, or impatience in suffering, as if there were no one near to help you; the Lord is at hand -- your help, your strength, your supply, your comfort is not far from you. In verse 6 of the same chapter we read, "Be careful for nothing; but in every thing by prayer and supplication with thanksgiving let your requests be made known unto God." This means, whatsoever your condition may be, do not afflict yourselves with anxieties, fear, and worries. Instead, bless the Lord for what you have, and pray for that which you lack; then, leave it to God, and so in patience, possess your souls.