Urwah narrates: Sayyidah Khadijah (may Allah be pleased with her) passed away three years, or about that, before the Prophet (peace and blessings be upon him) emigrated to Madinah, and he (peace and blessings be upon him) married Sayyidah Aishah (may Allah be pleased with her) close to the time of the death of Sayyidah Khadijah (may Allah be pleased with her).
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 19335