Undoubtedly, no one can be more truthful and honest than the Messengers of God. Muhammad proved by his living example that he was the most truthful and honest person of his age. Everyone was impressed by his honesty and truthfulness. 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. He was known as Al-Sadiq (the Truthful) and Al-Amin (the Faithful). Every Makkan, rich or poor called him by these names. When the dispute arose, among the various tribes of Makkah, as to who should lay the Black Stone in its proper place, in the Ka'bah, they decided that the one who entered the Ka'bah first next morning would place it. Muhammad was the first to enter the Ka'bah that morning and when the people saw him they were all very happy that Al-Amin and Al-Sadiq had come and would be the one to lay the Black Stone in its proper position.
Once the chiefs of the Quraish were sitting and talking about him. Nadhar bin Harith, the most experienced of them all, said, "O Quraish! 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."
When he gathered together all the Quraish near the Mount of Safa and asked them, "O Quraish! 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.
He had lived his whole life in purity and virtue among them and this was acknowledged even by his most staunch enemies. 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 God, when he did not tell lies against human beings! When the Qaiser of Rome received a letter from the Holy Prophet inviting him and his followers 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 the Qaiser. 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 God, he would not have abstained from speaking falsely against human-beings." The Qaiser then questioned him about the Prophet's general behaviour 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."
Muhammad practiced honesty in his life and preached honesty and truthfulness to others. Abu Sa'id Al-Khudri reported God's Messenger as saying, "Let not respect for men prevent any of you from speaking the Truth when he knows it."