Abu Dawud Book 14, Hadith Number 3130.

Narated By Anas ibn Malik : The Apostle of Allah (PBUH) passed Hamzah who was killed and disfigured. He said: If Safiyyah were not grieved, I would have left him until the birds and beasts of prey would have eaten him, and he would have been resurrected from their bellies. The garments were scanty and the slain were in great number. So one, two and three persons were shrouded in one garment. The narrator Qutaybah added: They were then buried in one grave. The Apostle of Allah (PBUH) asked: Which of the two learnt the Qur’an more? He then advanced him toward the qiblah (direction of prayer).