Muhammad proved by his living example that he was the most truthful and honest person of his age. He was a poor orphan who had started trading with his uncle, but in a very short time, owing to his honest and fair dealings with all people, he became well-known and respected. Every Makkan, rich or poor, knew him as As-Sadiq (the Truthful) and Al-Amin (the Trustworthy). When Muhammad was yet a young man, the Ka`bah was rebuilt. A dispute arose among the various tribes of Makkah as to who should have the honor of laying the Black Stone in its place in the Ka`bah. They decided that the first one to enter the Ka`bah the next morning would settle the dispute. Muhammad was the first to enter that morning and when the people saw him, they were all very happy that Al-Amin and As-Sadiq had come and would be the one to decide. He put the Black Stone on a cloth so that every tribe could hold the cloth and help to lift the stone, which he then set in place.
Once the chiefs of the Quraysh were sitting and talking about him. An-Nadar ibn al-Harith, the most experienced of them all, said, "O Quraysh! You have not been able to find any plan to meet the calamity that has fallen upon you. Muhammad grew up from childhood in your presence. He was the most liked, honest and faithful among you. Now when he has grown to maturity and has presented these things to you, you say, he is a magician, a soothsayer, a poet, a mad man. By Allah! I have heard his Message, he is none of these things. A new calamity has fallen upon you."
The Prophet once gathered together all the people of the Quraysh near Mount Safa and asked them, "O Quraysh! If I say that an army is advancing on you from behind the mountains, will you believe me?" All said in one voice, "Yes, because we have never heard you telling a lie." All the people of Makkah, without any exception, swore to his truthfulness and honesty, for he had lived an unblemished and extremely pious life among them for forty years. Yet most of them still refused to accept him as the Messenger of Allah.
He had lived his whole life in purity and virtue among them, and even his staunchest enemies acknowledged this. They knew that he was the most honest and truthful person among them. The Holy Qur'an, therefore, appealed to them to look at his life and try to understand. How could he tell lies against Allah, when he did not tell lies against human beings!
When the Byzantine Emperor Heraclius received a letter from the Prophet inviting him and his people to Islam, he called the Arab traders who were then visiting his country. He asked Abu Sufyan, their leader, "Did you ever find Muhammad telling a lie before his claim to Prophethood?" He replied that he had not. Then Heraclius said, "I asked you if he had ever told a lie and you replied that he had not. I am sure, if he had spoken unjustly against Allah, he would not have abstained from speaking falsely against human-beings." Heraclius then questioned him about the Prophet's general behavior and conduct with people. Abu Sufyan replied, "Muhammad is nobly born, is honest and truthful, and has never broken a pledge. He enjoins his followers to worship none but One God and to pray to Him alone. He preaches kindness, piety and tolerance towards all and his followers are on the increase."
The pagans of Makkah, though they rejected Muhammads call to Islam, still trusted none but him with their belongings when they traveled. When the Prophet finally escaped Makkah for Madinah, he asked his cousin `Ali to stay behind to return the pledges he was keeping. Trustworthy to all, he wouldnt keep even a pennys worth of his enemies property.