كتاب النكاح
16  
The Book of Marriage
(10)
Chapter: It is permissible for a father to arrange the marriage of a young virgin
(10)
باب تَزْوِيجِ الأَبِ الْبِكْرَ الصَّغِيرَةَ ‏
Sahih Muslim 1422 c

'A'isha (Allah be pleased with her) reported that Allah's Apostle (ﷺ) married her when she was seven years old, and he was taken to his house as a bride when she was nine, and her dolls were with her; and when he (the Holy Prophet) died she was eighteen years old.

وَحَدَّثَنَا عَبْدُ بْنُ حُمَيْدٍ، أَخْبَرَنَا عَبْدُ الرَّزَّاقِ، أَخْبَرَنَا مَعْمَرٌ، عَنِ الزُّهْرِيِّ، عَنْ عُرْوَةَ، عَنْ عَائِشَةَ، أَنَّ النَّبِيَّ صلى الله عليه وسلم تَزَوَّجَهَا وَهْىَ بِنْتُ سَبْعِ سِنِينَ وَزُفَّتْ إِلَيْهِ وَهِيَ بِنْتُ تِسْعِ سِنِينَ وَلُعَبُهَا مَعَهَا وَمَاتَ عَنْهَا وَهِيَ بِنْتُ ثَمَانَ عَشْرَةَ ‏.‏
Reference : Sahih Muslim 1422c
In-book reference : Book 16, Hadith 83
USC-MSA web (English) reference : Book 8, Hadith 3311
  (deprecated numbering scheme)