Ibn Majah

Benefits and Issues:
➊
The chief of martyrs, Hazrat Hamza, was the paternal uncle of the Messenger of Allah (sallallahu alayhi wa sallam), so it should have been permissible to marry his daughter. With this thought, Hazrat Ali (radi Allahu anhu) presented this suggestion, but the Messenger of Allah (sallallahu alayhi wa sallam) made it clear that although this relationship was possible in terms of lineage, it was not possible due to its being prohibited by reason of suckling (radā‘ah).

➋
Hazrat Hamza was breastfed by Abu Lahab’s slave woman, Thuwaibah. She also breastfed the Messenger of Allah (sallallahu alayhi wa sallam) for a few days. (Lum‘āt, Sharh Mishkāt, Kitāb al-Nikāh, Bāb al-Muḥarramāt) In this way, Hazrat Hamza became the foster brother (through suckling) of the Prophet (sallallahu alayhi wa sallam), and his daughter became the foster niece of the Prophet (sallallahu alayhi wa sallam).

➌
The name of this woman was Fatimah bint Hamza (radi Allahu anha). (Injāḥ al-Ḥājah, Ḥāshiyah Sunan Ibn Mājah by ‘Abd al-Ghani Dehlawi)

Hadith Commentary:
Hazrat Hamzah radi Allahu anhu and the Messenger of Allah sallallahu alayhi wa sallam both drank the milk of Thuwaibah, who was the slave woman of Abu Lahab. For this reason, Hazrat Amir Hamzah radi Allahu anhu was considered the foster brother of the Prophet sallallahu alayhi wa sallam.
One day, Abu Jahl caused harm to the Noble Messenger sallallahu alayhi wa sallam and also abused him verbally.
The slave woman of Hazrat Hamzah radi Allahu anhu narrated this incident to Hazrat Amir Hamzah radi Allahu anhu.
He, in anger, came before Abu Jahl and struck his head with a bow, breaking it, and said, "Here, I myself become a Muslim—now do whatever you wish to do." Thus, on that very day, Hazrat Hamzah radi Allahu anhu accepted Islam.
This incident took place in the sixth year of Prophethood. He was older than the Prophet sallallahu alayhi wa sallam in age, and he was martyred at Uhud.

Hadith Commentary:
(1)
Ali radi Allahu anhu once said to the Messenger of Allah sallallahu alayhi wa sallam:
“O Messenger of Allah! In terms of kinship, your inclination is towards the Quraysh.”
The Messenger of Allah sallallahu alayhi wa sallam replied:
“You have something that I would like.”
He (Ali) said:
“Marry the daughter of Hamzah radi Allahu anhu, who is your uncle’s daughter.”
He (the Prophet) replied:
“She is not lawful for me because she is the daughter of my foster brother.”
(Sahih Muslim, Al-Rada‘, Hadith: 3581 (1446))

(2)
Hamzah and the Messenger of Allah sallallahu alayhi wa sallam both drank the milk of Abu Lahab’s slave woman, Thuwaibah, and thus Hamzah radi Allahu anhu was your (the Prophet’s) foster brother, and in terms of lineage, your uncle.
Abu Salamah radi Allahu anhu also drank the milk of the slave woman Thuwaibah, so he too was the foster brother of the Prophet sallallahu alayhi wa sallam, as clarified in another hadith.
(Sahih al-Bukhari, Al-Nikah, Hadith: 5101)

(3)
There are various transmitted opinions regarding the name of Hamzah radi Allahu anhu’s daughter:
Imamah, ‘Ammarah, Salma, ‘A’ishah, Fatimah, Amatullah, and Ya‘la, etc.
Some historians have also mentioned Umm Fadl, but this is her kunyah (agnomen).
(Fath al-Bari: 178/9)

Hadith Footnote:
It is necessary to also consider fosterage (rada‘ah) in matters of relationship.

Explanation:
Hazrat Hamzah ibn Abdul Muttalib (radi Allahu anhu) was your (the Prophet’s, sallallahu alayhi wa sallam) uncle.
There was not much difference in age between the two.
Therefore, at the time when the Prophet (sallallahu alayhi wa sallam) was being breastfed, Hazrat Hamzah (radi Allahu anhu) was also in the same period of breastfeeding, and both of them were nursed by Abu Lahab’s slave woman, Thuwaibah.
Regarding Hazrat Hamzah’s (radi Allahu anhu) daughter, whose name is reported as either Umamah or ‘Ammarah, this hadith was narrated by you (the Prophet, sallallahu alayhi wa sallam) on this very basis.
Qastallani said: Among these, there are four relationships that are excepted—those that are prohibited by lineage, but not prohibited by fosterage (rada‘ah).
Their mention will come in the Book of Marriage (Kitab al-Nikah), insha’Allah Ta‘ala.

Hadith Commentary:
(1)
The Messenger of Allah (sallallahu alayhi wa sallam) and Hazrat Hamzah (radi Allahu anhu) both, in their childhood, drank the milk of Abu Lahab’s slave woman, Thuwaibah. Therefore, in terms of lineage, Hazrat Hamzah (radi Allahu anhu) was your uncle, but in terms of suckling (radā‘ah), he was your brother. Thus, marriage to a foster niece is not permissible.

(2)
It should be clear that marriage to the woman who breastfed (the child) and her mahrams is not permissible for the one who was breastfed, just as marriage to the mother and her mahrams is not permissible in lineage.
This generality does not apply from the child’s side, because if a woman breastfeeds a child, she undoubtedly becomes his mother, but it is permissible for the child’s father to marry her. Furthermore, there are four relationships that are prohibited due to lineage but are not prohibited due to suckling (radā‘ah); the details of which we will mention in the Book of Marriage (Kitab al-Nikah).

(3)
Imam Bukhari (rahimahullah) wants to establish that rulings can be derived from incidents that become well-known, just as the Prophet (sallallahu alayhi wa sallam) informed regarding the milk that he and Hazrat Hamzah (radi Allahu anhu) both drank from Thuwaibah.
The basis for this was also its fame among the people.
And Allah knows best.

English translation:

A niece is included among the mahram women, whether she is the daughter of a real (biological) brother or of a foster (milk) brother. Marriage with a sister, brother, and their offspring is absolutely forbidden (haram).