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.
Sahih al-Bukhari Book 63, Hadith 121
← Previous Hadith That the Prophet (ﷺ) said to her, "You have been shown to me twice in my dream. I saw you pictured on a piece of silk and some-one said (to me). 'This is your wife.' When I uncovered the picture, I saw that it was yours. I said, 'If this is from Allah, it will be done."

Sahih al-Bukhari Book 63, Hadith 120 Next Hadith → We visited Khabbaba who said, "We migrated with the Prophet (ﷺ) for Allah's Sake, so our reward became due and sure with Allah. Some of us passed away without taking anything of their rewards (in this world) and one of them was Mus`ab bin `Umar who was martyred on the day (of the battle) of Uhud leaving a striped woolen cloak. When we covered his head with it, his feet became naked, and when covered his feet, his head became naked. So Allah's Messenger (ﷺ) ordered us to cover his head and put some Idhkhir (i.e. a special kind of grass) on his feet. (On the other hand) some of us have had their fruits ripened (in this world) and they are collecting them."

Sahih al-Bukhari Book 63, Hadith 122