there is no killing the nafs. that isn't the goal. nor is it possible. The goal is to purify it and bring it into equilibrium, reform it, train it, guide it. Imam Ghazali describes it as training a horse. you don't beat the horse into submission, because then the horse will either be injured beyond being able to heal or it will fight back for his life. the method is to gradually train the horse to obey your command. Read Imam Ghazali's Disciplining the Soul in his Ihya. http://www.amazon.com/Al-Ghazali-Dis.../dp/0946621438