Sunan an-Nasa'i

It was narrated that Hisham bin 'Amir said: "We complained to the Messenger of Allah on the day of Uhud, saying: “O Messneger of Allah, it is too difficult for us to dig a grave for each person.' The Messenger of Allah said: “Dig graves and make them good and deep, and bury two or three in one grave.' They said: “Who should we put in first, O Messenger of Allah?' He said: “Put in first the one who knew more Qur'an."' He said: "My father was the third of three in one grave””””"