harer hārdam athāsinā
maṇiṁ jahāra mūrdhanyaṁ
Contradictory orders of different persons are impossible to carry out. Therefore a compromise was selected by Arjuna by his sharp intelligence, and he separated the jewel from the head of Aśvatthāmā. This was as good as cutting off his head, and yet his life was saved for all practical purposes. Here Aśvatthāmā is indicated as twice-born. Certainly he was twice-born, but he fell down from his position, and therefore he was properly punished.