Answer:
At the time of the marriage, the Prophet was twenty-five years old, while Khadijah was forty years old. She died after 15 years marriage (at age 55 years). Within these 15 years they lived happily together, and Khadijah bore several children. Their first child, a son whom they named Qasim, died when he was only two years old. Two more sons, called Tayyib and Tahir, were also born, but they too died in their infancy. However, Muhammad and Khadijah also had four daughters who survived: Zaynab, Ruqayya, Umm Kulthum and Fatima.