Khadijah bint Khuwaylid or Khadījah al-Kubra (Khadijah the Great) was the first wife and follower of the Prophet Muhammad. She is regarded by Muslims as the “Mother of the Believers”. Khadijah is regarded as one of the most important female figures in Islam, like her daughter, Fatimah. Muhammad was monogamously married to her for 25 years. After the death of Khadijah, Muhammad re-married.
Khadijah (RA) was the closest to Muhammad and he confided in her the most out of all his following wives. It is narrated in many hadiths that Khadijah was Muhammad’s most trusted and favorite among all his marriages. It is narrated in Sahih Muslim: The messenger of Allah said: “God Almighty never granted me anyone better in this life than her. She accepted me when people rejected me; she believed in me when people doubted me; she shared her wealth with me when people deprived me; and Allah granted me children only through her. ‘A’ishah (RA) narrated of Muhammed and Khadijah in Sahih Bukhari: “I did not feel jealous of any of the wives of the Prophet as much as I did of Khadijah though I did not see her, but the Prophet used to mention her very often, and when ever he slaughtered a sheep, he would cut its parts and send them to the women friends of Khadijah. When I sometimes said to him, “(You treat Khadijah in such a way) as if there is no woman on Earth except Khadijah,” he would say, “Khadijah was such-and-such, and from her I had children. It is also narrated: The Messenger of Allah said: “The best of its women is Khadijah bint Khuwailid, and the best of its women is Maryam bint ‘Imran. Muhammad said about her “She believed in me when the whole world refuted me and she attested to my veracity when the whole world accused me of falsehood. She offered me compassion and loyalty with her wealth when everyone else had forsaken me.” Khadeeja (RA) was the daughter of Khuwaylid ibn Asad, who was the great-grandson of Qusai ibn Kilab.
Khadijah (RA) was the first female and person to become a follower of Muhammad. Muhammad was married to her until her death and Khadijah was the only wife to be married to Muhammad in monogamy, thus sometimes regarded as Muhammad’s most beloved. She is regarded as one of the most important women in Islam, and in terms of the progression of Islam, the most important out of all of Muhammad’s wives.
Source:https://en.wikipedia.org/wiki/Khadija_bint_Khuwaylid