Hear no ill of a friend, nor speak any of an enemy.

Related:

• If you would keep your secret from an enemy, tell it not to a friend.
  - Ben...
• Ill customs and bad advice are seldom forgotten.
  - Ben...
• Fear to do ill, and you need fear nought else.
  - Ben...
• Hear reason, or she'll make you feel her.
  - Ben...
• Neither trust, nor contend, nor lay wagers, nor lend;
  and you'll have peace to your lives' end. -- Ben...
• Proclaim not all thou knowest, all thou owest, all thou hast,
  nor all thou can'st. -- Ben...
• Teach your child to hold his tongue; he'll learn fast enough to speak.
  - Ben...
• When you speak to a man, look on his eyes; when he speaks to thee,
  look on his mouth. -- Ben...
• Be civil to all; sociable to many; familiar with few;
  friend to one; enemy to none. -- Benjamin...