The Ansar came to the Messenger of Allah ﷺ on the day of Uhud and said: We have been afflicted with wound and fatigue. What do you command us? He said: Dig graves, make them wide, bury two or three in a single grave. He was asked: Which of them should be put first? He replied: The one who knew the Qur'an most. He (Hisham) said: My father Amir died on the day and was buried with two or one.  

جَاءَتِ الأَنْصَارُ إِلَى رَسُولِ اللَّهِ ﷺ يَوْمَ أُحُدٍ فَقَالُوا أَصَابَنَا قَرْحٌ وَجَهْدٌ فَكَيْفَ تَأْمُرُنَا قَالَ احْفِرُوا وَأَوْسِعُوا وَاجْعَلُوا الرَّجُلَيْنِ وَالثَّلاَثَةَ فِي الْقَبْرِ قِيلَ فَأَيُّهُمْ يُقَدَّمُ قَالَ أَكْثَرُهُمْ قُرْآنًا قَالَ أُصِيبَ أَبِي يَوْمَئِذٍ عَامِرٌ بَيْنَ اثْنَيْنِ أَوْ قَالَ وَاحِدٌ  

"And deepen (the graves)."  

عَنْ حُمَيْدِ بْنِ هِلاَلٍ بِإِسْنَادِهِ وَمَعْنَاهُ زَادَ فِيهِ وَأَعْمِقُوا  

This tradition has also been transmitted by Sa'd b. Hisham b. 'Amir with a different chain of narrators.  

عَنْ سَعْدِ بْنِ هِشَامِ بْنِ عَامِرٍ بِهَذَا الْحَدِيثِ