Bukhari

Hadith Commentary:
Its meaning is that the Prophet (sallallahu alayhi wa sallam) did not spend the entire night sleeping, nor did he spend the entire night awake and engaged in worship.
Every night, he would both sleep and worship, so whoever wished to see him in any particular state could see him as such.
Some people think that staying awake and worshipping the entire night, or always fasting, is greater than the worship of the Prophet (sallallahu alayhi wa sallam).
They do not realize that by staying awake all night or by always fasting, the soul (nafs) becomes accustomed to it, and then there remains no hardship in worship for it.
The real difficulty is that one maintains the habit of sleeping at night, as well as the habit of eating and drinking during the day, and then, by exerting effort over the soul, breaks its habit whenever one wishes.
To turn away from sweet sleep.
Thus, what the Prophet (sallallahu alayhi wa sallam) did is what is superior, what is higher, and what is more difficult.
He had nine wives; the Prophet (sallallahu alayhi wa sallam) fulfilled their rights, fulfilled the rights of his own soul,
fulfilled the rights of his relatives and of the general Muslims as well.
Along with all this, he also worshipped Allah; tell me, how great a heart and courage is required for this!
To take a staff, tie up one's loincloth, and sit alone in seclusion, and to become carefree and detached—this is very easy for the soul.

Hadith Commentary:
(1)
From this narration, Imam Bukhari rahimahullah has established the non-obligation of the night prayer (tahajjud) upon the Messenger of Allah sallallahu alayhi wa sallam, because it is proven from this that sometimes he would spend the entire night sleeping. If standing in prayer at night (qiyam al-layl) had been obligatory, he would certainly have adhered to it. (Fath al-Bari: 3/29)

(2)
The meaning of this hadith is that the nine voluntary prayers (nafl) of the Messenger of Allah sallallahu alayhi wa sallam at night and his being engaged in rest occurred at different times of the night. Whoever wished to see him in any particular state could do so. This is the personal observation of Anas radi Allahu anhu, which does not contradict the statement of Aisha radi Allahu anha that he would wake up upon hearing the crowing of the rooster, because she described what she herself witnessed, and the Prophet sallallahu alayhi wa sallam would generally perform the night prayer at home, whereas the hadith of Anas radi Allahu anhu is understood to refer to other circumstances. Both narrated their own observations regarding the Messenger of Allah sallallahu alayhi wa sallam. (Fath al-Bari: 3/31)

(3)
Imam Bukhari rahimahullah himself has narrated this corroboration (mutaba‘at) of Abu Khalid Ahmar with a connected chain. (Sahih al-Bukhari, al-Sawm, Hadith: 1973) From the narration of Sulayman, it is known that the narrator Humayd asked Anas radi Allahu anhu about the fasting of the Messenger of Allah sallallahu alayhi wa sallam, so he narrated this hadith. (Sahih al-Bukhari, al-Sawm, Hadith: 1972)