Nasai

Commentary:
Burying in a spacious grave will be easier and the grave will be protected from collapsing, therefore this is recommended (mustahabb).

Explanation:
1:
That is, the noble Companions made this complaint:
O Messenger of Allah, we are wounded and battered,
we are not in a condition to prepare separate graves for the martyrs.
In such a situation, what do you command us to do?
Because digging separate graves is proving to be difficult.

Benefits and Issues:
➊
The noble Companions (radi Allahu anhum ajma'in) were wounded and exhausted, yet despite this, they were commanded to make the graves deep, as is explicitly mentioned in the following narration.
➋
If there are many deceased, it is permissible to bury more than one person in a single grave.
➌
A Hafiz of the Qur'an, a reciter, and a scholar of religion remain superior and distinguished from others even after death.

Benefit:
This statement of the Messenger of Allah (sallallahu alayhi wa sallam) was made at the time of the burial of the martyrs of the Battle of Uhud.
He (sallallahu alayhi wa sallam) said:
Dig the graves spacious, deep, and well, and bury two or three (individuals) in one grave.
And the one who knows more of the Qur'an should be placed ahead (towards the Qiblah).
(Sunan an-Nasa'i, Al-Jana'iz, Chapter: What is recommended regarding widening the grave, Hadith: 2013)

(1) "It is very difficult" because there were many martyrs, and the remaining people were wounded and disheartened by this great loss. In such a condition, to dig seventy graves in one day was extremely difficult. Even in a state of peace, making so many graves is a very difficult task.

(2) "Dig deep" because in this way the deceased will be much more protected from animals, rain, etc., and there will also be no danger of the grave collapsing.

(3) In case of necessity, more than one person may be buried in a single grave, but it is necessary that the shroud (kafan) be separate for each. However, a woman should not be buried with a non-mahram; though there is no harm in burying a mother and her child together.

For details, see Hadith: 2012.

Knowledge is a distinctive quality of human beings; therefore, among humans, the basis of superiority is knowledge. And the Noble Qur’an is the original source of knowledge; thus, the Prophet (sallallahu alayhi wa sallam) made it the criterion of superiority.