Bukhari

Hadith Commentary:
Nawawi said: The Prophet (sallallahu alayhi wa sallam) would place his saliva on his index finger, put it on the ground, and recite this supplication, then he would have that soil applied to the site of the wound or pain, and by Allah’s command, healing would occur.

Hafiz (rahimahullah) says: “And this is from the aspect of seeking blessing (tabarruk) through the names of Allah, the traces of His Messenger, and as for placing the finger on the earth, perhaps it is due to a particular property in that, or due to a wisdom in concealing the effects of divine power by means of engaging with customary causes.” (Fath)

That is, this is to seek blessing with the blessed names of Allah and with the traces of His Messenger (sallallahu alayhi wa sallam), and as for placing the finger on it, perhaps it is due to a particular property in that, or there is some hidden wisdom of the effects of divine power in it, which aligns with apparent causes. By “the traces of the Messenger” is meant that finger which he (sallallahu alayhi wa sallam) would place on the earth, apply soil, and recite the supplication.

Artificial traces are not intended.

Hadith Commentary:
(1)
In one narration, it is mentioned that the Messenger of Allah (sallallahu alayhi wa sallam) would place his saliva on his finger and recite the aforementioned supplication for the recovery of the sick.
(Sunan Ibn Majah, Book of Medicine, Hadith: 3521)
Both the soil of Madinah Tayyibah and the saliva of the Messenger of Allah (sallallahu alayhi wa sallam) possess a special honor; however, whoever acts upon this Sunnah in this manner, inshaAllah, the sick person will be cured.

(2)
Saliva and soil are apparent means which have been commanded to be utilized; the occurrence of healing in them is dependent upon the permission of Allah, the Exalted.
The saliva of a believer and soil, regardless of which land it is from, are a part of the means of healing.
The real effect in this is in the words “bi-idhni rabbina” (“by the permission of our Lord”).
Qadi Baydawi writes that, according to the research of medicine, saliva has a significant role in changing the temperament, and the soil of one’s homeland has a remarkable effect in preserving temperament and repelling harm.
The people of medicine say that a traveler would keep some soil from his homeland with him; when he encountered unsuitable water, he would put a little soil into the water-skin so that he would be protected from the negative effects of that place.
In reality, there are wondrous effects in ruqyah (incantations and blowing); the intellect is incapable of comprehending their true nature.
(Fath al-Bari: 10/257)

Hadith Commentary: Benefits and Issues: This hadith establishes that Allah, the Exalted, has connected a person’s temperament with his region, and He has placed an effect even in human saliva, which—by the blessing of Allah’s name, and if Allah wills—becomes a means of healing for boils, abscesses, and wounds.

Benefits and Issues:
➊ In Sahih al-Bukhari, at the beginning of this supplication, the word (Bismillah) appears, and instead of (bariqa), the word (wariqa) is mentioned.
(Sahih al-Bukhari, Book of Medicine, Hadith: 5746)
➋ Imam Nawawi rahimahullah states that the person performing ruqyah should moisten his finger with his saliva, then apply soil to it, and then pass it over the afflicted area or over the patient while reciting these words.

Benefits and Issues:

➊ The soil of Madinah and the blessed saliva of the Messenger of Allah (sallallahu alayhi wa sallam) both possess a special honor. However, whoever acts in this manner with the intention of following the Sunnah, insha Allah, the sick person will be cured.

➋ Hafiz Salahuddin Yusuf (hafizahullah) writes regarding this: Saliva and soil are apparent means, which we have been commanded to utilize. The effect of healing being produced in them is by the permission of Allah. In reality, this is a prescribed (masnun) supplication (dam). The real effect lies in the words “by the permission of our Lord” (bi-idhni rabbina). The saliva of a believer’s mouth and the soil, whether from any land, are only a part of this healing. And through experience, the great effectiveness of this supplication has been proven. (: Riyad as-Salihin, Hadith: 901)

Benefit:
The permissibility of performing ruqyah (incantation) is established from this hadith. When performing ruqyah on a boil or wound, the index finger used in tashahhud should be placed on the ground, and after reciting this supplication, the finger should be applied to the wound.