An excellent article on how Mohammad's moral example being less than impeccable.
Includes the following reference from the Sahih Al-Bukhari:
Volume 7, Book 62, Number 88: Narrated ‘Ursa:
The Prophet wrote the (marriage contract) with ‘Aisha while she was six years old and consummated his marriage with her while she was nine years old and she remained with him for nine years (i.e. till his death).