Bukhari

Explanation:
By mentioning this chain of narration, the purpose of Imam rahimahullah is to establish that Humayd actually heard (this hadith) from Anas radi Allahu anhu, and thus the statement of Yahya ibn Sa'id al-Qattan is proven incorrect—that Humayd heard this hadith from Thabit, who heard it from Abu Nadrah, who heard it from Anas. From this, it is understood that if, while performing prayer (salah), one spits into a piece of cloth so that neither the prayer is disrupted nor a nearby place is soiled, then this is permissible and correct.

Hadith Commentary:
The purpose of the honorable Imam rahimahullah in mentioning this chain of narration is to establish that Humayd actually heard (this hadith) from Anas radi Allahu anhu, and to refute the statement of Yahya ibn Sa'id al-Qattan that Humayd heard this hadith from Thabit.

He (i.e., Humayd) narrated from Abu Nadrah, who narrated from Anas.

From this, it is understood that if, while performing prayer, one spits into a piece of cloth so that neither is the prayer disrupted nor is a nearby place soiled, then this is permissible and correct.

Hadith Commentary:
1.
A clarification is being made regarding "aqdhar," which is the plural of "qadhar."
A detestable thing is called "qadhar."
There are two types of it:
* That which is both detestable and impure (najis), such as urine, feces, semen, etc.
* That which, despite being detestable, is not impure, such as saliva, phlegm, and sweat, etc.
In this chapter, Imam al-Bukhari is stating the ruling regarding those "aqdhar" which are detestable but not impure.
The need to mention this arose because Salman al-Farsi (radi Allahu anhu) and Ibrahim al-Nakha'i (rahimahullah) considered saliva and the moisture that flows from the nose to be impure once separated from the mouth and nose.
On this issue, Imam al-Bukhari (rahimahullah) is in agreement with the majority, that saliva and phlegm, etc., are pure; if they get on clothing, the clothing does not become impure.
Similarly, if these things fall into water, the water does not become impure because of them.
It is another matter that their use may be repugnant to others, but it is not necessary that every repugnant thing be impure.
Hafiz Ibn Hajar (rahimahullah) has written, referencing Ibn Hazm, that according to Salman al-Farsi (radi Allahu anhu) and Ibrahim al-Nakha'i, saliva is impure provided it separates from the mouth.
(Fath al-Bari: 1/459)

2.
Allamah 'Ayni has written:
There is some detail regarding saliva: if the mouth is pure, then the saliva will also be pure, and if the saliva is from a person who has consumed alcohol, then at that time his saliva will also be impure and his leftover (food or drink) will also be impure.
('Umdat al-Qari: 2/681)

3.
Marwan's father accepted Islam on the day of the Conquest of Makkah. For certain reasons, the Messenger of Allah (sallallahu alayhi wa sallam) exiled him. Marwan also went with him to Ta'if.
During his caliphate, 'Uthman (radi Allahu anhu) summoned both the father, Hakam, and the son, Marwan, to Madinah al-Tayyibah.
Marwan was not present at the event of Hudaybiyyah, so what is the status of the narration attributed to him? The answer is that the original narration is from Miswar (radi Allahu anhu), and Marwan's narration has been added as corroboration. However, the objection still remains: what is the meaning of strengthening a narration with the report of someone who was not present at the event? It is possible that Marwan heard this narration regarding the Treaty of Hudaybiyyah from another Companion.
And Allah knows best.
The detailed narration will be mentioned in the chapter on the Treaty of Hudaybiyyah.

4.
The reason the Messenger of Allah (sallallahu alayhi wa sallam) spat into a garment was that he saw spit stuck to the wall in the mosque, so he said that if there is a need to spit during prayer, one should spit to one's left or under one's feet. Then he spat on the corner of his cloak, joined its edges, and said that this can also be done. However, spitting into a garment is in the case when there is a need for quick relief, as Imam al-Bukhari (rahimahullah) has established a chapter in the Book of Prayer (Bab 39) with these words:
(If saliva overcomes him, let him take hold of the edge of his garment.)
"If saliva overcomes him, let him spit into a corner of his cloak."
Although this is not evident from the aforementioned hadith, in a narration of Sahih Muslim, this is clarified.
(Fath al-Bari: 1/465)
Since that narration did not meet Imam al-Bukhari's (rahimahullah) criteria, he only alluded to it in the chapter heading.
(Sahih Muslim, Hadith: 1228(550))
In light of these ahadith, it is understood that if the need arises during prayer, instead of collecting it in the mouth, one should spit to the left, and if someone is praying on the left, then spit under one's feet, and if it is overwhelming, then spit into one's garment and fold it.
However, in current circumstances, instead of spitting to the left or under the feet, the method of spitting into the garment is the only appropriate one.
And Allah knows best.

Sufyan al-Thawri rahimahullah is narrating this hadith of Sahih al-Bukhari «عن».

Some people object to the narration on the authority of ‘an, saying: “Prove explicit audition (sama‘) or corroboration (mutaba‘ah).”

(4) In Sahih al-Bukhari, Bab al-Buzaq wa al-Mukhat, vol. 1, p. 38 (hadith 241), in this narration, Isma‘il ibn Ja‘far has corroborated Sufyan. Also, in Sahih al-Bukhari, Kitab al-Salat, Bab Hak al-Buzaq bi’l-Din min al-Masjid (hadith 405).

Reference: Fatawa ‘Ilmiyyah (Tawdih al-Ahkam), vol. 2, p. 315