(26) The Book of Marriage
كتاب النكاح
(29) Chapter: A Man Marrying Off His Young Daughter
(29) باب إِنْكَاحِ الرَّجُلِ ابْنَتَهُ الصَّغِيرَةَ ‏.‏
Sunan an-Nasa'i 3257 
It was narrated that Abu 'Ubaidah said:
"Aishah said: 'The Messenger of Allah married me when I was nine and I lived with him for nine years.'"
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا عَبْثَرٌ، عَنْ مُطَرِّفٍ، عَنْ أَبِي إِسْحَاقَ، عَنْ أَبِي عُبَيْدَةَ، قَالَ قَالَتْ عَائِشَةُ تَزَوَّجَنِي رَسُولُ اللَّهِ صلى الله عليه وسلم لِتِسْعِ سِنِينَ وَصَحِبْتُهُ تِسْعًا ‏.‏
Grade :  Sahih (Darussalam)
Reference : Sunan an-Nasa'i 3257
In-book reference : Book 26, Hadith 62
English translation : Vol. 4, Book 26, Hadith 3259