It was narrated from a freed slave of 'Aishah that:
'Aishah said: "I never looked at (or I never saw) the private part of the Messenger of Allah." (Da'if)(One of the narrators) Abu Bakr (Ibn Abu Shaibah) said: "Abu Nu'aim would say: '(From) a freed female slave of 'Aishah.'" (IT)
English reference (IT): Vol. 1, Book 1, Hadith 662 (IT)
Arabic reference (IT): Book 1, Hadith 707 (IT)