The Messenger of Allah ﷺ used to wrap two of the slain at Uhud together in a single garment, then he would ask, "Which of them had memorized more of the Quran?" When one of them was indicated, he placed him first in the grave. He said, "I will be a witness over these on the Day of Resurrection." He ordered that they be buried in their blood, and they were neither washed nor prayed over.
أخبرنا قتيبة قال حدثنا الليث عن ابن شهاب عن عبد الرحمن بن كعب بن مالك أن
أن رسول الله ﷺ كان يجمع بين الرجلين من قتلى أحد في ثوب واحد ثم يقول أيهما أكثر أخذا للقرآن فإذا أشير إلى أحدهما قدمه في اللحد قال 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, no. 1343, from the hadith of Layth bin Saad, and in the Book of Military Expeditions, chapter on those Muslims who were killed on the day of..., no. 4079, from Qutayba through him, and it is in Al-Kubra, no. 2082.