Musnad Abu Ya'la al-Mawsili 109:14

Narrated to us Ishaq, narrated to us Abd al-Razzaq, informed us Ma'mar, from al-Zuhri, from Ibn Abi Sa'ir, from Jabir, who said: When the day of Uhud arrived, the Prophet, may Allah bless him and grant him peace, looked over the martyrs who were martyred on that day and said: "Wrap them in their blood, for I am a witness over them." So, two or three men would be buried in a single grave. He would ask, "Which of them was more learned in the Quran?" and he would place him forward. Jabir said: So my father and my uncle were buried on that day in one grave.