After his encounter with the angel Jibreel (aS) in the cave of Hira, Muhammad ﷺ rushed home, not knowing what to make of the encounter. He was comforted by his wife Khadijah (rA), who believed his account. She asked her cousin, who was familiar with Jewish and Christian scriptures, what this could mean. When he heard of what happened, he immediately accepted Muhammad ﷺ as the messenger of his time, like Moosa and Eesa (aS) before him. Muhammad ﷺ accepted his mission as the Messenger of Allah, and his life as the Prophet began.
Source: Lost Islamic History (Pg. 11)