Bukhari

Hadith Commentary:

There are twelve hours in the night, so they would sleep during the first six hours, then worship for four hours, and then sleep for two hours.
It is as if they would be sleeping at the time of suhoor; this is the very translation of the chapter heading.

Hadith Commentary:
(1)
The meaning of this hadith is that if the night consists of twelve hours, then Dawud (alayhis salam) would sleep for the first six hours, then he would worship for a third of the night, that is, four hours, and after that, for a sixth of the night, that is, two hours, he would again rest. In other words, he would spend the time of suhoor (pre-dawn) in sleep.

(2)
The purpose of the above heading is that a person who remains asleep at the time of suhoor is not blameworthy, provided that he has already fulfilled the rights of the night (i.e., worshipped during the night).
The wisdom in sleeping at this time is that one may attain freshness for the morning prayer (salah) and remove fatigue, etc.
Doing so is also a means of protection from showing off (riya), because a person who worships at night and then sleeps, by the time he wakes up, the traces of worship will have disappeared from his face.
(Fath al-Bari: 3/23)

Benefit:
In this hadith, among the supererogatory fasts, the most virtuous fast is declared to be the fast of Dawud (alayhis salam), that is, to fast one day and leave (not fast) the next day. Whoever Allah, the Exalted, grants such strength to, may act upon this; otherwise, in supererogatory matters, the Shari‘ah does not impose hardship upon anyone, but rather only encourages (good deeds).

Furthermore, in this hadith, among the supererogatory prayers, the most virtuous prayer is declared to be the prayer of Dawud (alayhis salam): he would sleep for half the night, then stand (in prayer) for a third of it, and then sleep for a sixth of it—Subhan Allah.

In this manner, sleep is also completed, and supererogatory worship is also performed abundantly. The worship of some misguided people is contrary to the Sunnah; whether the worship is little or much, it should be ensured that it is in accordance with the Qur’an and Hadith.

Benefit:
From this hadith, it is understood that a person who spends the entire night in standing (prayer) and fasts every day should be reproached; instead of being praised, he should be criticized, because a believer does not fall short in fulfilling the rights of the servants (huquq al-‘ibad) alongside the rights of Allah (huquq Allah).