Bukhari

Hadith Commentary:
What happened was that Sa’d ibn Abi Waqqas radi Allahu anhu was the governor of Kufa on behalf of Umar radi Allahu anhu.
There, the people of Banu Asad complained to Umar radi Allahu anhu about him, saying that he did not know how to perform the prayer properly.
Sa’d radi Allahu anhu refuted them, saying: “If I have not learned how to pray until now, even though I am among the earliest Muslims—when I accepted Islam, there were only six people who had become Muslim—then how have you people learned to pray, when you only became Muslim recently?”
All the complaints of Banu Asad were false, and their objecting to Sa’d radi Allahu anhu was like “a small mouth making a big claim.” To find fault with the elders is itself a mistake (Wahidi).

Hadith Commentary:
(1)
Sa’d ibn Abi Waqqas radi Allahu anhu was among the earliest to embrace Islam. When Umar radi Allahu anhu appointed him as the governor of Kufa, the people there complained about him, alleging that he did not perform the prayer properly and did not act with justice and fairness when making judgments. This angered him, for how could a person who was among the earliest Muslims be negligent regarding the rulings of the Shari’ah? He said, “If today I am in need of the instruction and discipline of Banu Sa’d, then my previous deeds have been wasted, for we accepted Islam in extremely difficult circumstances, at a time when we survived on the leaves of trees.” In any case, none of the complaints of Banu Sa’d were based on reality.

(2)
Imam Bukhari rahimahullah, through this hadith, has described the food of the earliest Companions radi Allahu anhum, that in those days there was no abundance of food and drink; rather, these noble individuals would fill their stomachs with the leaves of trees, which would cause them severe constipation, and when relieving themselves, only hard droppings would come out.