The Prophet ﷺ used to wrap two of those slain at Uhud in a single cloth, then he would ask, "Which of them had memorized more of the Quran?" When one was pointed out to him, he placed that one first in the grave and 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.
كان النبي ﷺ يجمع بين الرجلين من قتلى أحد في ثوب واحد ثم يقول: أيهم أكثر أخذا للقرآن؟ فإذا أشير له إلى أحدهما قدمه في اللحد وقال: أنا شهيد على هؤلاء يوم القيامة وأمر بدفنهم في دمائهم، ولم يغسلوا، ولم يصل عليهم.
Bukhari related it in the Book of Funerals (1343) from Abdullah bin Yusuf, who said, Layth narrated to us, who said, Ibn Shihab narrated to me from Abdul-Rahman bin Kaab bin Malik from Jabir, and he mentioned it.There are other hadiths on this subject that have already been mentioned in the Book of Funerals.