Bukhari

Explanation:
In order to acquire the knowledge of the noble hadith, the Prophet sallallahu alayhi wa sallam praised Abu Hurairah radi Allahu anhu. From this, the virtue of the Ahl al-Hadith is established. The meaning of "from the heart" is that one should avoid shirk (associating partners with Allah), because whoever does not avoid shirk is not truly affirming this statement with his heart, even if he recites it with his tongue. This is just as is the case nowadays with many so-called Muslims who are worshippers of graves.

Hadith Commentary:
1.
Imam Bukhari rahimahullah previously mentioned the encouragement for seeking knowledge in general; now he brings a hadith regarding the virtue of the knowledge of hadith.
Linguistically, "hadith" refers to something new; since the Noble Qur’an is eternal, in comparison, hadith is something new. In the terminology of the hadith scholars (muhaddithin), the definition of hadith is:
Every statement, action, approval, or character trait that is attributed to the Messenger of Allah sallallahu alayhi wa sallam.
Abu Hurairah radi Allahu anhu had a special devotion to the knowledge of hadith.
He himself states that his Ansari brother would be occupied with farming, and the Muhajirun would be busy with their businesses, while he would always remain in the service of the Messenger of Allah sallallahu alayhi wa sallam, lest he miss any of his words or actions. Once, Abu Hurairah radi Allahu anhu complained to the Messenger of Allah sallallahu alayhi wa sallam about forgetfulness, so the Messenger of Allah sallallahu alayhi wa sallam spread out his cloak, recited something over it, and then said:
“O Abu Hurairah radi Allahu anhu, gather it to your chest.”
As a result, his chest became a treasury of hadiths.
(Sahih al-Bukhari, Kitab al-‘Ilm, Hadith: 119)
2.
On the Day of Resurrection, the intercession (shafa‘ah) of the Messenger of Allah sallallahu alayhi wa sallam will occur in various forms:
➊ Intercession for the elevation of ranks and raising of stations.
➋ Intercession for entry into Paradise without reckoning or punishment.
➌ Intercession for the alleviation of the punishment of Hellfire.
➍ Intercession for the removal of some believers from Hell.
➎ Intercession for saving those deserving of the Fire from punishment.
➏ Intercession for deliverance from the terrors of the Gathering (Mahshar).
3.
The meaning of uttering the word of sincerity (kalimah ikhlas) from the heart is that one does not associate anyone with Allah, for whoever commits shirk, his claim is merely verbal and not affirmed by the heart. Among them, the one most deserving of intercession will be the one who recited the kalimah with sincerity.

Hadith Commentary:
He said it with sincerity of heart and put it into practice, remaining steadfast upon tawhid (monotheism) throughout his life, and not even a trace of shirk (associating partners with Allah) touched him.
Surely, such a person will attain intercession, and by the blessing of tawhid and his practical striving, his sins will be forgiven.
May Allah, the Exalted, grant all of us this felicity.
Ameen.

Hadith Commentary:
(1)
He recited the kalimah of tawhid (the declaration of Allah’s oneness) with sincerity of heart, then acted according to its requirements. He remained steadfast upon it his entire life, never allowing even a trace of disbelief (kufr) or polytheism (shirk) to touch him. Certainly, such a person will attain the intercession (shafa‘ah) of the Messenger of Allah sallallahu alayhi wa sallam. By the blessing of tawhid and through practical striving, effort, and diligence, all his sins will be forgiven.

(2)
It appears that Abu Hurairah radi Allahu anhu asked this question at the time when the Messenger of Allah sallallahu alayhi wa sallam narrated the following hadith:
“Every prophet had a supplication that was answered (certainly accepted), which he made in this world, but I wish to reserve my supplication for the intercession of my ummah in the Hereafter.” (, Sahih al-Bukhari, Kitab al-Da‘awat, Hadith: 6304)
In another narration, it is stated that the one most entitled to my intercession will be the person who testifies to la ilaha illallah (there is no god but Allah) with sincerity. His heart affirms what his tongue says, and his tongue affirms what is in his heart. (Musnad Ahmad: 307/2)
Then, those who attain the blessing of intercession will have varying ranks, as indicated by the word “as‘ad” (most fortunate). (Fath al-Bari: 539/11)