Bukhari

Hadith Commentary:

On one occasion, the Messenger of Allah (sallallahu alayhi wa sallam) placed his hand on the chest of Abdullah bin Aslam (radi Allahu anhu) and said, "Say!" He did not understand what to say. Then he (the Prophet) said again, "Say!" So he recited: "Qul huwa Allahu ahad" (Say: He is Allah, the One). The Prophet (sallallahu alayhi wa sallam) said, "Say!" again, so he recited: "Qul a'udhu bi-Rabbil-falaq" (Say: I seek refuge with the Lord of the daybreak). The Prophet (sallallahu alayhi wa sallam) again said the same, so he recited: "Qul a'udhu bi-Rabbin-nas" (Say: I seek refuge with the Lord of mankind). The Prophet (sallallahu alayhi wa sallam) then said: "Seek refuge in this way, for there are no other surahs for seeking refuge like these."

Hadith Commentary:
The apparent wording of this hadith indicates that the Messenger of Allah (sallallahu alayhi wa sallam) would first blow onto his hands and then recite the Mu'awwidhat (the last two chapters of the Qur'an). However, no one holds this view, nor is there any benefit in it, because after reciting and then blowing, one can hope for blessing. It is possible that the intent behind this was to oppose the practices of magicians, because they blow after reciting, whereas the Prophet (sallallahu alayhi wa sallam) blew before reciting. (Umdat al-Qari: 13/559) According to our preferred view, the method of ruqyah (spiritual healing) is that after reciting the Mu'awwidhat, one should blow, so that healing may be hoped for through the blessed breaths. And Allah knows best.

Hadith Commentary:
Reciting these surahs and performing ruqyah (incantation) with them is Sunnah. May Allah, the Most Pure, protect everyone from all prevalent innovations and polytheistic forms of ruqyah, and grant every Muslim the good fortune to make the supplications established from the Sunnah their regular practice. Ameen.

Hadith Commentary:
(1)
This refers to the illness during which the Prophet sallallahu alayhi wa sallam passed away.
In the beginning, he sallallahu alayhi wa sallam would perform ruqyah (spiritual healing) himself, but when the illness intensified, he instructed Aisha radi Allahu anha, and she would perform ruqyah for him.

(2)
Imam Bukhari rahimahullah has established from the word "nafh" (blowing) that after reciting the Mu'awwidhat (the last two chapters of the Qur'an), he sallallahu alayhi wa sallam would blow onto his hands in such a way that a small amount of saliva would also be included.
Some individuals are of the opinion that there should be no nafh (blowing with slight spittle) during ruqyah, but this view is not correct, as we have already explained earlier.
In one hadith, it is mentioned that on the day of Khaybar, Salamah bin Akwa' radi Allahu anhu was injured, so people said, "Salamah is finished." I was brought to the Messenger of Allah sallallahu alayhi wa sallam, and he blew on me three times, in which there was a slight amount of saliva, and after that, I have never experienced any pain from it.
(Sahih al-Bukhari, al-Maghazi, Hadith: 4206)

Explanation:
1:
They are called "Mu'awwidhat" because through them, refuge is sought from Allah, Lord of all worlds.
It is understood from this that these chapters should be recited at bedtime so that one attains Allah's protection during sleep.

Benefits and Issues:
Reciting the last three surahs as a protective supplication (dam) at bedtime is a cure for many outward and inward illnesses, especially the evil eye, magic, and satanic influences.
This is on the condition that a person practices it regularly with faith and conviction.