Bond of Brotherhood
Nevertheless, following the migration, the Holy Prophet (sa) formed a bond of brotherhood between Hazrat Hamza (ra) and Hazrat Zaid (ra) bin Harithah. On this very basis, Hazrat Hamza (ra) made a will in the name of Hazrat Zaid (ra) while they were on their way to participate in the Battle of Uhud.
(At-Tabaqat Al-Kubra Li Ibn Sa‘d, Vol. 3, p.6, Hamza bin Abdil Muttalib, Darul-Kutub Al-‘Ilmiyyah, 1990, Beirut)