शत्रुसेविनि मित्रे च गूढे युक्ततरो भवेत् । गतप्रत्यागते चैव स हि कष्टतरो रिपुः ॥ १८६ ॥
Let him be very much on his guard against a friend who secretly serves the enemy and against (deserters) who return (from the enemy’s camp); for such (men are) the most dangerous foes.