It was narrated from Abu Hurairah that:
The Prophet met 'Uthman at the door of the mosque and said: "O 'Uthman! Jibril has told me that Allah married you to Umm Kulthum for a dowry like that of Ruqayyah, provided that you treat her as you treated Ruqayyah." (IT)
English reference (IT): Vol. 1, Book 1, Hadith 110 (IT)
Arabic reference (IT): Book 1, Hadith 115 (IT)