Sunan Ibn Majah, Chapter: Chapters Regarding Funerals

that the Messenger of Allah (saw) used to put two or three of the slain of Uhud in one shroud. He would ask: "Which of them had memorized more Quran?" And if one of them was pointed out to him, he would put him in the niche-grave first. And he said: "I am a witness over them." He commanded that they should be buried with their blood, and that the funeral prayer should not be offered for them and they should not be washed. Sahih