Hazrat Abbaas (radhiyallahu ‘anhu) mentions, “The first person to pledge allegiance at the blessed hands of Rasulullah (sallallahu ‘alaihi wasallam) was Hazrat As’ad bin Zuraarah (radhiyallahu ‘anhu) (who was the most fortunate). Thereafter, Hazrat Baraa bin Ma’roor (radhiyallahu ‘anhu) pledged allegiance, and then Hazrat Usaid bin Hudhair (radhiyallahu ‘anhu).”

(In order to further strengthen this pledge), Hazrat Abbaas bin Ubaadah (radhiyallahu ‘anhu) addressed the Khazraj and said, “O people of Khazraj! Do you realise what you are pledging? Understand that you are pledging to wage war with the Arabs and the non-Arabs. If you have the slightest thought that in future, when faced with devastating catastrophes, you would apprehensively abandon this, then you might as well give up now. By Allah! To abandon the pledge then, out of fear, will be a source of humiliation in this world as well as the next. If, however, you are prepared to suffer the adversities of the future, you are willing to sacrifice your wealth and lives, and you are eager to remain staunch upon this pledge, then by Allah, this will be a source of your success and fortune in this world as well as in the next.”

In one voice, they all agreed, “Yes, we are pledging our allegiance upon this! We are not reluctant to sacrifice our wealth and lives for Rasulullah (sallallahu ‘alaihi wasallam)! By Allah! Even if we are faced with calamities, we can never violate this pledge!” 

(Extracted from Seeratul Mustafa 1/342-343)