A Muslim? Is the boy a Muslim? It would be foolish to let him live:

1) The boy will grow up and become just as ruthless a warrior and killer as his people.
2) The fact that you save him will only fuel anger and hatred in his heart for the humiliation you inflicted by saving him. Or do you think he can live knowing that as an adult, warriors will spit in his face and shout that he is a slave of the infidel who saved him?
3) The boy will die anyway. Without food, in a burned-out city, at the age of six. From illness, cold, hunger, or the sword of another Crusader.
4) It would be more merciful to send him to heaven; children's souls are pure, regardless of whether they are Christian or