Ibn Majah

Explanation:
He was called the uncle’s son figuratively. In reality, he was the cousin of their father, i.e., the cousin of Zayn al-Abidin, because Muhammad ibn al-Hanafiyyah was the brother of Hasan and Husayn (radi Allahu anhuma), who is the father of Hasan, who had asked this question from Jabir (radi Allahu anhu). The correspondence between the chapter heading and the narrations mentioned is evident: the Messenger of Allah (sallallahu alayhi wa sallam) would pour water over his blessed head three times during the ritual bath (ghusl) of major impurity. Thus, this is the prescribed (sunnah) method. From this, it is also established that the practice of the Noble Messenger (sallallahu alayhi wa sallam) is, in every circumstance, worthy of being followed.

Hadith Commentary:
➊
Hazrat Jabir (radi Allahu anhu) said that although the Messenger of Allah (sallallahu alayhi wa sallam) had more hair than you and was more fond of cleanliness, even then he poured water on his head three times and sufficed with that amount. From this, it is understood that cleanliness and purification are certainly achieved with this quantity.
To consider cleanliness dependent on more than this is a sign of self-admiration, or it is due to doubt and misgivings, which should not be given importance.
(Fath al-Bari: 1/478)

➋
From this, it is understood that one should ask scholars about matters related to religion, and a scholar should not be stingy in giving answers. Likewise, the seeker of truth should have the attitude that when the truth becomes clear, he should not make excuses or arguments in accepting it.
(‘Umdat al-Qari: 3/24)

➌
From this, it is understood that the question of Hasan ibn Muhammad is different from the question mentioned by Abu Ja‘far; in both incidents, the one addressing Hazrat Jabir (radi Allahu anhu) is Hasan ibn Muhammad.
In the previously mentioned incident, he objected to the quantity of water, saying that such an amount is not sufficient for him, and here he objected to the manner, saying that in this way his hair does not become clean.
At the time of the first incident, Abu Ja‘far was present, whereas at the time of this incident, he was not present.
(Fath al-Bari: 1/478)

➍
Hazrat Jabir (radi Allahu anhu) calling Hasan ibn Muhammad the cousin of Abu Ja‘far is metaphorical, because in reality, he is the cousin of Abu Ja‘far al-Baqir’s father, Zayn al-‘Abidin, on the basis that Zayn al-‘Abidin is the son of Hazrat Husayn (radi Allahu anhu), and Hasan is the son of Muhammad ibn al-Hanafiyyah, who is the son of Hazrat Ali (radi Allahu anhu). Thus, Hazrat Husayn and Muhammad ibn al-Hanafiyyah are paternal brothers.
Therefore, Hasan is not the cousin of Abu Ja‘far, but rather the cousin of his father, Zayn al-‘Abidin, and Hazrat Jabir (radi Allahu anhu) metaphorically referred to him as Abu Ja‘far’s cousin.
(Fath al-Bari: 1/478)

➎
A woman named Hanafiyyah was the wife of Hazrat Ali (radi Allahu anhu), whom he married after the death of Hazrat Fatimah (radi Allahu anha). From her, a son named Muhammad was born, and he became more famous by his mother’s name than his father’s.
It is said that most of his life was spent with Yazid ibn Mu‘awiyah; for this reason, or perhaps people did not consider it good to attribute him to Hazrat Ali (radi Allahu anhu) so that familial rivalry with Hazrat Ali (radi Allahu anhu) would remain.
And Allah knows best.
It is this Muhammad’s son, Hasan, who debates and discusses with Hazrat Jabir (radi Allahu anhu) regarding ritual bath (ghusl).

Explanation:
The person speaking was Hasan ibn Muhammad ibn Hanafiyyah. Hazrat Jabir radi Allahu anhu admonished him sternly. From this, it is understood that those who make frivolous objections against hadith should be admonished strictly, and it is in no way permissible to employ personal opinion, analogy (qiyas), or interpretation (ta'wil) in opposition to hadith.

«والحنفية كانت زوجة على تزوجها بعد فاطمة فولدت لها محمدا فاشتهربالنسبة اليها .» [فتح الباري]

That is, the woman named Hanafiyyah was the wife of Hazrat Ali radi Allahu anhu, whom he married after the passing of Sayyidah Fatimah radi Allahu anha. From her womb, a child named Muhammad was born, and he became more well-known by his mother’s name rather than his father’s.

Hadith Commentary:
➊
In the narration, Abu Ja‘far refers to Hazrat Baqir, whose name is Muhammad bin Husayn bin Ali bin Abi Talib rahimahullah.
His father is Hazrat Zayn al-‘Abidin Ali bin Husayn. In reality, there was some disagreement among these individuals regarding the ritual bath (ghusl) of the Messenger of Allah sallallahu alayhi wa sallam, so they presented themselves before Hazrat Jabir radi Allahu anhu to investigate the matter. The one who asked the question was only Hazrat Baqir, but since all of them desired clarification, the question was attributed to all of them collectively.
When Hazrat Jabir radi Allahu anhu explained that one sa‘ (a specific measure) is sufficient for the ritual bath (ghusl), a person present in the gathering said that such a small amount is insufficient for the ritual bath.
The one who said this was Hazrat Hasan, the son of Hazrat Muhammad bin Hanafiyyah. Since his manner was not appropriate, Hazrat Jabir radi Allahu anhu, in a tone of admonition, said: “This amount may not be sufficient for you; perhaps you have more hair on your head or you are excessively cautious.”
But for the Messenger of Allah sallallahu alayhi wa sallam, this amount was sufficient, even though he had more hair on his blessed head than you.
Moreover, he was extremely cautious in every matter, so the only reason for insufficiency could be that you are excessive in your use of water.
From this hadith, it is also understood that there is no harm in sternly explaining to someone who disputes against the hadith.
(Fath al-Bari: 1/475)

➋
According to this narration, Hazrat Abu Ja‘far Baqir asked Hazrat Jabir radi Allahu anhu about the amount of water required for the ritual bath (ghusl), to which Hazrat Jabir radi Allahu anhu replied that one sa‘ is sufficient.
Hasan bin Muhammad bin Hanafiyyah said that it would not be sufficient for him, and this was also answered.
Further, Hasan bin Muhammad bin Hanafiyyah’s question regarding the manner of performing the ritual bath (ghusl) is mentioned: What is the method of the ritual bath for major impurity (janabah)? Hazrat Jabir radi Allahu anhu replied that the Messenger of Allah sallallahu alayhi wa sallam would take three handfuls of water and pour them over his head, then pour water over his entire body. Upon this, Hasan bin Muhammad said, “I have a lot of hair.”
Hazrat Jabir radi Allahu anhu replied, “The Prophet sallallahu alayhi wa sallam had more hair than you.”
(Sahih al-Bukhari, al-Ghusl, Hadith: 256)

Hadith Commentary:
Isma‘ili has added that Shu‘bah says: The Messenger of Allah (sallallahu alayhi wa sallam) used to do this in the ritual bath (ghusl) for major impurity (janabah). When Jabir (radi Allahu anhu) narrated this hadith, a man from Banu Hatim said:
“My head hair is very thick.”
Jabir (radi Allahu anhu) replied:
“The hair of the Messenger of Allah (sallallahu alayhi wa sallam) was more and better than your hair.”
(Sahih al-Bukhari, Hadith: 252)
From this it is understood that pouring water over the head three times during the ritual bath (ghusl) for major impurity (janabah) is sufficient, even if the person performing the bath has a lot of hair on his head.
(‘Umdat al-Qari: 21/3)