(44) باب تَزْوِيجُ النَّبِيِّ صلى الله عليه وسلم عَائِشَةَ وَقُدُومُهَا الْمَدِينَةَ وَبِنَاؤُهُ بِهَا
Narrated Hisham's father:
Khadija died three years before the Prophet (ﷺ) departed to Medina. He stayed there for two years or so and then he married `Aisha when she was a girl of six years of age, and he consumed that marriage when she was nine years old.
Reference: Sahih al-Bukhari 3896
In-book reference: Book 63, Hadith 122
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 5, Book 58, Hadith 236