Musnad Abu Ya'la al-Mawsili 118:33

Abu Bakr ibn Abi Shaybah narrated to us, Ubayd Allah ibn Musa narrated to us, from Usamah ibn Zayd, from al-Zuhri, from Anas, who said: When the day of Uhud arrived, the Messenger of Allah (ﷺ) passed by Hamzah, and his nose had been cut off and he had been mutilated. He said: "Were it not that Safiyyah would find [grief] in herself, I would have left him until Allah gathers him from the bellies of the beasts and the birds." He was shrouded in a striped garment; when his head was covered, his feet were exposed, and when his feet were covered, his head was exposed. So they covered his head. He did not perform the funeral prayer over any of the martyrs, and he said: "I am a witness over you today." He used to gather three in one grave and two in one grave, and he would ask: "Which of them was more learned in the Quran?" Then he would place him forward in the *lahd* (niche). And he would shroud two or three men in a single garment.