According to Ibn Ishaq, the Holy Prophet (sa) gave his daughter, Hazrat Ruqayyah (ra), in marriage to Hazrat Uthman (ra). Hazrat Ruqayyah (ra) passed away during the days of the Battle of Badr. Following this, the Holy Prophet (sa) gave his other daughter – Hazrat Umm Kulthum (ra), the sister of Hazrat Ruqayyah (ra) in marriage to Hazrat Uthman (ra). As such, he became known as Dhun-Nurain [possessor of two lights].
(Ibn Hajar al-Asqalani, Al-Isabah fi Tamyiz al-Sahabah, Vol. 4, Uthman (ra) bin Affan [Beirut, Lebanon: Dar al-Kutub al-Ilmiyyah, 2004], p. 377)