Some members in the gathering wanted to come to Abu Jahal’s defense, but he himself prevented them saying, “Today I spoke very harshly and badly to his nephew. Leave Hamzah alone.”
Some of those present addressed Hazrat Hamzah (radhiyallahu ‘anhu) saying, “O Hamzah! Have you also become a Saabi (abandoned the religion of your forefathers)?” Hazrat Hamzah (radhiyallahu ‘anhu) replied, “The truthfulness and honesty of Muhammed (sallallahu ‘alaihi wasallam) has become absolutely clear to me. I testify that Muhammed (sallallahu ‘alaihi wasallam) is the Rasul of Allah and that whatever he says is absolutely true. I will never forsake his deen. You may do whatever you wish.” Saying this, Hazrat Hamzah (radhiyallahu ‘anhu) returned home.
(Seeratul Mustafa 1/182-183)