Bond of Brotherhood
With regard to the bond of brotherhood that was formed with Hazrat Ali (ra), it is mentioned in the narrations that the Holy Prophet (sa) declared Hazrat Ali (ra) to be his brother on two occasions. On one occasion, the Holy Prophet (sa) formed bonds of brotherhood between the Muhajireen in Mecca and later the Holy Prophet (sa) formed bonds of brotherhood between the Muhajireen and Ansar after having migrated to Medina. On both occasions, the Holy Prophet (sa) said to Hazrat Ali (ra):
اَنْتَ اَخِيْ فِي الدُّنْيَا وَالْآخِرَة
“You are my brother, in this world as well as in the Hereafter!”
(Ali Ibn al-Athir, Usd al-Ghabah fi Ma‘rifat al-Sahabah, Vol. 4, Dhikr Ali bin Abi Talib [Beirut, Lebanon: Dar al-Kutub al-Ilmiyyah, 2016], 88)
According to another narration, the Holy Prophet (sa) formed a bond of brotherhood between Hazrat Ali (ra) bin Abi Talib and Hazrat Sahl (ra) bin Hunaif.
(Ibn Saad, Al-Tabaqat al-Kubra, Vol. 3, Dhikr Ali bin Abi Talib [Beirut, Lebanon: Dar al-Kutub al-Ilmiyyah, 2017], 16)
According to the historical references, this bond was formed on two occasions. A commentator of Sahih Bukhari, Allama Qastallani, states that the bond of brotherhood was formed on two occasions. Firstly, in Mecca, prior to the migration, where the Holy Prophet (sa) formed bonds of brotherhood between Hazrat Abu Bakr (ra) and Hazrat Umar (ra) and between Hazrat Uthman (ra) and Hazrat Abdur Rahman(ra) bin Auf and between Hazrat Zubairra and Hazrat Abdullah (ra) bin Masud and between Hazrat Ali (ra) and himself. Following this, and after having migrated to Medina, the Holy Prophet (sa) formed bonds of brotherhood between the Muhajireen and the Ansar at the house of Hazrat Anas (ra) bin Malik.
Ibn Saad relates that the Holy Prophet (sa) formed bonds of brotherhood between a hundred companions; that is, between 50 Muhajireen and 50 Ansar.
(Irshad al-Sari Sharh Sahih al-Bukhari, Vol. 8, pp. 410-411, Hadith 3937, Dar al-Kutub al-Ilmiyyah, 1996)