Sa'd bin Hisham bin Amir narrates from his father (Hisham bin Amir, may Allah be pleased with him) that in the Battle of Uhud the wounds were severe, and this was complained of to the Messenger of Allah (peace and blessings be upon him). He (peace and blessings be upon him) said: "Make the graves wide and make them well, and bury two or three in one grave."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6754