Proverbs 27:17 in the King James Version
Iron sharpeneth iron; so a man sharpeneth the countenance of his friend.
Context
16 restraining her is like restraining the wind, or like grasping oil in his right hand.
17 Iron sharpens iron; so a man sharpens his friend’s countenance.
18 Whoever tends the fig tree shall eat its fruit. He who looks after his master shall be honored.