Bulugh al-Maram

Lexical Explanation:
«الْحَدُوا» is the imperative form from «فَتحَ يَفْتَحُ». "Lahd" refers to the grave's niche dug towards the qiblah side.
«وَانْصِبُوا» is the imperative form from «ضَرَبَ يَضْرِب».
It is in the meaning of «اقِيمُوا», i.e., to set up, to erect.
In «اَللَّبِنَ», the "lam" has a fatha and the "ba" has a kasrah beneath it. It refers to a brick made from clay. When it is baked in fire, it is called «اَجُرَ», with a dammah on the "jeem" and a shaddah on the "ra".
«قَدْرَ شِبْرٟ» has a kasrah beneath the "sheen" and the "ba" is sakin. It is the distance from the tip of the thumb to the tip of the little finger, i.e., a span.
«اَنْ يُّجَصَّصَ الْقَبْرُ» is derived from tahsis and is in the passive form, meaning to construct with lime.
«وَاَّنْ يُّبنٰي عَلَيْهِ» is in the passive form, meaning that no structure should be built over the grave for the purpose of making it high and prominent, nor should any structure like a dome be built around the grave.

Benefits and Issues:
Several rulings are illuminated by this hadith:
➊ The grave should not be higher than one span.
➋ In the blessed era of the Messenger of Allah sallallahu alayhi wa sallam, there were two methods of preparing graves: one was lahd (niche) and the other was shaq (trench). Lahd, i.e., the side niche, is made by first digging a pit and then making a space on the qiblah side within it to place the deceased. Shaq means digging a large pit and then digging a relatively smaller pit in the middle for the deceased. Both methods are proven to be permissible from the mentioned ahadith, as narrated from Anas bin Malik radi Allahu anhu, who said: When the Prophet sallallahu alayhi wa sallam passed away, there was a man in Madinah who used to make lahd graves and another who used to make shaq (straight) graves. The Companions radi Allahu anhum said: We seek guidance from our Lord (pray for the better option) and call both of them; whichever one remains behind, we will leave him (and the one who comes first will prepare the grave in his manner). So both were sent for, and the one who made lahd arrived first, so the Companions radi Allahu anhum had a side-niche grave prepared for the Prophet sallallahu alayhi wa sallam. [مسند احمد : 139/3 واسنن ابن ماجه ، الجنائز باب ماجاء فى الشق ، حديث : 1558 ، 1557]
Also, it is narrated from Abdullah bin Abbas radi Allahu anhuma that the Messenger of Allah sallallahu alayhi wa sallam said: "Lahd is for us, and shaq is for others." [سنن ابي داود ، الجنائز ، باب فى اللحد ، حديث : 3208]
The scholars explain that the meaning of "shaq is for others" is not that it is not permissible for us; rather, it likely means that non-Muslims mostly use the shaq grave, while Muslims mostly make lahd (side-niche) graves.
Imam Nawawi rahimahullah writes regarding this that making a lahd is recommended because the Companions radi Allahu anhum unanimously dug a lahd for the Messenger of Allah sallallahu alayhi wa sallam. See: [صحيح مسلم بشرح النووي ، الجنائز : 49 ، 48/7 ۔ حديث : 966]
Therefore, where the ground is firm and a lahd (side-niche) grave can be made, lahd is recommended and superior; however, making a shaq (box-type) grave is also permissible, as this is also proven from the ahadith, «والله اعلم»
➌ Unbaked bricks should be used inside.
➍ Building any kind of structure over the grave and making the grave solid is prohibited in the Shariah, and this prohibition is of a binding (tahrimi) nature.
➎ It is also not correct to give the grave any specific shape. The eternal resting place of the Prophet sallallahu alayhi wa sallam was hump-shaped and not higher than one span, and this is also the condition of the graves of Abu Bakr and Umar radi Allahu anhuma.