Urwah bin al-Zubayr said: Sayyidah Khadijah (may Allah be pleased with her) died 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 death of Sayyidah Khadijah, and he did not marry anyone else in addition to Sayyidah Khadijah while she was alive, until she passed away.
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 19298