Bukhari

Hadith Commentary:

He had no children; Anas was his nephew, which is why he described himself as his heir. This includes scholarly inheritance as well. The commentators write:

"And We have inherited him" is a refutation of those who say that Abu Zayd is Sa'd 'Ubayd al-Awsi, because our lineage is Khazraj, so Abu Zayd is one of his paternal uncles who inherited him—how could he be from the Aws, as is mentioned in the virtues according to the narration of Qatadah: I said to Anas, 'Who is Abu Zayd?' He said, 'He is one of my paternal uncles.' (Bukhari Commentary)

In summary, Abu Zayd is one of the uncles of Anas; he is not Sa'd 'Ubayd al-Awsi, because Anas is Khazraji, not Aws. Therefore, those who have taken Sa'd 'Ubayd al-Awsi to be meant by Zayd are mistaken in their view.

Hadith Commentary:
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This hadith is different from the previous hadith narrated from Anas radi Allahu anhu.
Firstly, in this narration, it is stated restrictively that at the time of the passing of the Messenger of Allah sallallahu alayhi wa sallam, there were only four memorizers of the Qur'an (huffaz), and secondly, in this narration, instead of Ubayy ibn Ka'b radi Allahu anhu, Abu Darda radi Allahu anhu is mentioned.

➋
In any case, at the time of the passing of the Messenger of Allah sallallahu alayhi wa sallam, numerous companions radi Allahu anhum ajma'in were memorizers of the Qur'an.
Regarding the Ansar specifically, it is explicitly stated that in addition to the aforementioned individuals, 'Ubada ibn Samit and Abu Ayyub al-Ansari radi Allahu anhu were also memorizers of the Qur'an.
Similarly, among the Muhajirun, several individuals were memorizers of the Qur'an, foremost among them being Abu Bakr radi Allahu anhu.
The Messenger of Allah sallallahu alayhi wa sallam honored him with the position of leadership in prayer (imamah), and for imamah, it is necessary to have greater recitation of the Qur'an.
And Allah knows best.