The Messenger of Allah ﷺ used to gather two or three of those slain at Uhud in a single garment, then he would ask, "Which of them had memorized the most of the Quran?" When one of them was pointed out to him, he would place that one first in the grave. He said, "I am a witness over these men." He ordered that they be buried in their blood, and they were neither washed nor prayed over.
حدثنا محمد بن رمح أنبأنا الليث بن سعد عن ابن شهاب عن عبد الرحمن بن كعب بن مالك
أن رسول الله ﷺ كان يجمع بين الرجلين والثلاثة من قتلى أحد في ثوب واحد ثم يقول أيهم أكثر أخذا للقرآن فإذا أشير له إلى أحدهم قدمه في اللحد وقال أنا شهيد على هؤلاء وأمر بدفنهم في دمائهم ولم يصل عليهم ولم يغسلوا
Bukhari narrated it in the Book of Funerals, Chapter on the Prayer over the Martyr, hadith no. 1343, and others narrated it as well, from the hadith of Layth, with the same wording.