As Rasulullah grew older, his good manner and truthfulness became well known to all his friends and the people of Makkah. He was noted for his honesty. The people of Makkah respected him and called him AL-AMEEN (the trustworthy). The people left their goods with him for safe keeping. But Rasulullah was disgusted with the people doing wrong around him and he often went to a cave called Hira. He spent his time there in the remembrance of Allah.
A rich widow of Makkah, Khadija by name, hearing about Rasulullah's honesty and truthfulness, asked him to go to Syria for her on a business trip. When Rasulullah came back he gave an account for every dirham. Hazrat Bibi Khadija (R.A.) was completely won over by his honesty and good manners.
Contents of the biography of the Prophet Muhammed