With regard to the title of Hazrat Uthman (ra), it is said that during the age of ignorance, it was Abu Amr. After his son, Abdullah, was born to him through Hazrat Ruqayyah (ra), the daughter of the Holy Prophet (sa), he became known by the title of Abu Abdillah among the Muslims.
(Ali Muhammad al-Salabi, Sirat Amir al-Momineen Uthman (ra) bin Affan Shakhsiyyatuhu wa Asruh, Ch. 1 [Beirut, Lebanon: Dar al-Ma‘rifah, 2006] p. 15)