Use your enemy's hand to catch a snake.

Related:

• Always use your enemy's hand to catch a
  snake...
• Trust in God - but tie your camel tight. --
  Persian...
• Doubt is the key to knowledge. --
  Persian...
• Never try to catch two frogs with one hand. --
  Chinese...
• Contempt penetrates even the shell of the tortoise.
  Persian...
• The blind man is laughing at the bald head.
  Persian...
• A snake deserves no pity.
  Yiddish...
• He who wants a rose must respect the thorn.
  Persian...
• The enemy of my enemy is my friend
  Arab...