Hazrat Yazid bin Roomaan (rahimahullah) narrates:
Hazrat ‘Uthmaan (radhiyallahu ‘anhu) and Hazrat Talhah (radhiyallahu ‘anhu) had proceeded, after Hazrat Zubair bin ‘Awwaam (radhiyallahu ‘anhu) had accepted Islam, until they entered into the blessed presence of Rasulullah (Sallallahu ‘alaihi wasallam). Rasulullah (Sallallahu ‘alaihi wasallam) invited them to Islam, recited a portion of the Qur’aan Majeed to them, informed them of the rights of Islam, and promised them to receive honor from Allah Ta‘ala if they upheld the Deen of Islam. They both brought Imaan and accepted the message of Rasulullah (Sallallahu ‘alaihi wasallam).
Hazrat ‘Uthmaan (radhiyallahu ‘anhu) then said, “O Rasul of Allah (Sallallahu ‘alaihi wasallam)! I arrived recently from Shaam. (While we were travelling from Shaam,) when we were between Mu‘aan and Zarqaa’, we were as if asleep when we heard a person announce, ‘O people who are asleep! Wake up, for Ahmed (Sallallahu ‘alaihi wasallam) has appeared in Makkah Mukarramah!” When we thereafter arrived in Makkah Mukarramah, we heard of you (claiming to be the Nabi of Allah Ta‘ala).”
Hazrat ‘Uthmaan (radhiyallahu ‘anhu) had accepted Islam in the very early days, before Rasulullah (sallallahu ‘alaihi wasallam) had entered Daar-ul-Arqam.
(Ibn Sa’d 3/40)