It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that Sayyidah Khadijah (may Allah be pleased with her) bore the Messenger of Allah (peace and blessings be upon him) six children: Abdullah, al-Qasim, Ruqayyah, Umm Kulthum and Fatimah (may Allah be pleased with them), and Mariyah al-Qibtiyyah (may Allah be pleased with her) bore him (peace and blessings be upon him) Ibrahim.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12063