Bukhari Collection: ::Book Number 4:: Hadith # 697
Narrated Kulaib bin Wail:I asked Zainab bint Abi Salama (i.e. daughter of the wife of the Prophet, "Tell me about the Prophet . Did he belong to the tribe of Mudar?" She replied, "Yes, he belonged to the tribe of Mudar and was from the offspring of An-Nadr bin Kinana."