Rejoice in the Lord alway: and again I say, Rejoice. Let your moderation be known unto all men. The Lord is at hand.Be careful for nothing; but in every thing by prayer and supplication with thanksgiving let your requests be made known unto God. And the peace of God, which passeth all understanding, shall keep your hearts and minds through Christ Jesus.

-Bible (NewTestament)
Philippians 4:4^7.

I distrust a man that says when. If he's got to be careful not to drink too much it's because he's not to be trusted when he does.

-Hammett, (Samuel) Dashiell
  The Maltese Falcon,'The Fat Man'.

So careful of the type she seems, So careless of the single life.

-Tennyson
  Of Nature. In Memoriam A.H.H., canto 55, l.7^8.

   A man cannot be too careful in the choice of his enemies.

-Wilde, Oscar Fingal O'FlahertieWills
The Picture of Dorian Gray, ch.1.