They hide within themselves that which they disclose not unto thee , saying : had we aught of the affair , we would not have been slain here . Say thou : had ye stayed in your houses , even then those decreed to be slain would surely have gone forth to their places of slaughter ; and this happened in order that he might prove that which was in your breasts , and purge that which was in your hearts ; and Allah is Knower of that which is in the breasts .