Bukhari

Hadith Commentary:
Performing ablution (wudu) before sleeping, placing one’s right hand under the right cheek and lying on the right side, and reciting the prescribed supplications or any one of them are highly emphasized Sunnahs.
It is better that after reciting the supplication, no conversation takes place.
And Allah knows best.

Hadith Commentary: Seeking blessing and assistance through the name of Allah has been established; this is the relevance to the chapter.

Hadith Commentary:
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In these hadiths as well, the method of supplicating by means of Allah’s names is described: that a person seeks blessing from Allah’s name at the time of sleep and wakefulness, and presents himself before Allah, saying that even in the state of wakefulness, I remember only Your name.
It is through this very name that I attain tranquility, and my heart finds rest through this name alone.
By virtue of this, I am granted a beneficial life.
Similarly, in the state of sleep, I invoke only Your name; through it, grant me peace and tranquility in every condition.
The Prophet (sallallahu alayhi wa sallam) used to recite this supplication at the time of sleeping, because sleep is a kind of death, and in contrast, wakefulness is a form of life and a great blessing from Allah upon His servants.

➋
Sometimes it is possible that the soul may not return in the state of sleep.
But when, after sleep, life is restored, vigor and strength return; in such a state, the aforementioned supplication has been taught in order to express gratitude to Allah.
At one place, Allah the Exalted has referred to sleep as death.
The statement of Allah the Exalted is:
“It is Allah who takes away the souls at the time of their death, and those that do not die, He takes their souls during their sleep. Then He withholds those for whom He has decreed death and sends the others back for an appointed term. Surely in this are signs for people who reflect.” (: al-Zumar 39/42)