Bond of Brotherhood
When the Holy Prophet (sa) established the bonds of brotherhood in Mecca between the Muhajireen, he established a bond between Hazrat Zubair (ra) and Hazrat Abdullah bin Mas‘ud (ra). After the migration to Medina, the bond of brotherhood with the Ansar was established between Hazrat Zubair (ra) and Hazrat Salma bin Salaama (ra).
(Usdul Ghaba, Vol. 2, p. 307, Zubair bin al-Awwam (ra), Dar-ul-Kutub al-Ilmiyyah, Beirut, 2003)