According to the narration of Mustadrak Haakim, when Hazrat Hamzah (radhiyallahu ‘anhu) appeared before Rasulullah (sallallahu ‘alaihi wasallam), he declared:

أشهد أنك لصادق شهادة المصدق والعارف

I give the testimony of one who has belief and knows what he is testifying to that you are definitely the true Nabi.

He then said, “O my nephew! You may proclaim your deen in public. By Allah! Even if I am offered the whole world and whatever is contained in it, I will not renounce your religion and prefer the religion of my forefathers.”

(Extracted from Seeratul Mustafa 1/183-184)