Bukhari

Hadith Commentary:
Abdullah bin Amir bin Rabi’ah was not originally from the Banu ‘Adi tribe, but he was their ally (halif), which is why he was referred to as being from Banu ‘Adi.
In some manuscripts, instead of Banu ‘Adi, it is written as Banu Amir bin Rabi’ah.
Among all the sons of the well-known Companion, Abdullah was the eldest.
It is said that he was born during the blessed era of the Prophet (sallallahu alayhi wa sallam).
‘Ajli has declared him trustworthy (thiqah).
The hadith mentions the elders who participated in Badr, and this is the reason for its relevance to the chapter.
Hazrat Qudamah bin Maz’un (radi Allahu anhu), who is mentioned in the narration, was the governor of Bahrain during the era of Farooq (i.e., the caliphate of Umar radi Allahu anhu), but later Hazrat Umar (radi Allahu anhu) dismissed him and appointed Hazrat Uthman bin Abi al-‘As (radi Allahu anhu) as the governor of Bahrain.
Hazrat Qudamah (radi Allahu anhu) was accused of consuming an intoxicating substance, and Hazrat Umar (radi Allahu anhu) heard this complaint.
When this crime was proven, Hazrat Umar (radi Allahu anhu) established the prescribed punishment (hadd) upon him and dismissed him from his post.
Then it so happened that during the journey of Hajj, Hazrat Qudamah accompanied Hazrat Umar (radi Allahu anhu).
One night, Hazrat Umar (radi Allahu anhu) woke up hurriedly from sleep and said, “Immediately bring Qudamah to me. Just now, someone came to me in a dream and said that I should reconcile with Qudamah (radi Allahu anhu).
You and he are Islamic brothers.”
Thus, Hazrat Umar (radi Allahu anhu) reconciled with him and removed the previous resentment from his heart.
(Qastallani)

Hadith Commentary:
➊
From this hadith, Imam Bukhari rahimahullah has established that Amir bin Rabi’ah and Qudamah bin Maz’un radi Allahu anhuma were participants in the Battle of Badr (Badri Companions).
Qudamah bin Maz’un radi Allahu anhu’s sister, Zaynab bint Maz’un, was the honorable wife of Umar radi Allahu anhu, and Umar’s sister, Safiyyah bint Khattab, was married to Qudamah bin Maz’un radi Allahu anhu. On this basis, the two were brothers-in-law to each other, and Qudamah radi Allahu anhu was the maternal uncle of Abdullah bin Umar radi Allahu anhu and Umm al-Mu’minin Safiyyah radi Allahu anha.
(‘Umdat al-Qari: 12/56)

➋
Qudamah bin Maz’un radi Allahu anhu was the governor of Bahrain during the caliphate of Umar radi Allahu anhu. A complaint was received regarding his consumption of alcohol, so Umar radi Allahu anhu dismissed him and appointed Uthman bin Abi al-‘As radi Allahu anhu as the governor there. Then, after the crime was proven, the prescribed punishment (hadd) was carried out upon him. It so happened that during the Hajj journey, both of them were together.
One night, Umar radi Allahu anhu woke up early and said:
“Bring Qudamah to me.
I have been instructed in a dream to reconcile with him; he is my brother in Islam.” Thus, Umar radi Allahu anhu removed any resentment from his heart and reconciled with him.
(Fath al-Bari: 7/400)