Qatadah said: Sayyidah Khadijah (may Allah be pleased with her) died in Makkah three years before the Hijrah, and she was the first of all men and women to believe in the Prophet (peace and blessings be upon him). He (peace and blessings be upon him) married no one other than her in the time of Jahiliyyah, and among his free wives, none other than her bore him (peace and blessings be upon him) children.
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 19299