Mus'ab bin Umayr was a missionary and a great orator of Islam who had been sent by the Prophet to Yathrib on the request of As'ad bin Zurarah. These two persons decided to invite the chiefs of Yathrib to Islam by means of logical argument.
One day they entered a garden where some Muslims were present and Sa'd bin Ma'az and Usayd bin Huzayr, who were the chiefs of Bani Abdul Ashhal, could also be seen there. Sa'd turned towards Usayd and said: "Unsheathe your sword and go to these two men and tell them to desist from propagating the religion of Islam and not to deceive our simple-minded people with their speeches and narrations. As As'ad bin Zurarah is my cousin (maternal aunt's son) I feel shy of facing him with a naked weapon".
Usayd stood in the way of the two men with an angry face and a naked sword and uttered the above-mentioned words with a harsh voice. The great orator Mus'ab bin Umayr who had learnt the method of propagation from the Prophet addressed Usayd thus: "Is it possible that you should sit with us for a while so that we may have mutual conversation. If what we say is disagreeable to your mind, we shall return the way we have come". Usayd said: "You have said something reasonable".
He, therefore, sat down for a moment and sheathed his sword. Mus'ab recited a few verses of the Qur'an. The luminous realities of the Qur'an and their attraction and sweetness coupled with the forceful logic of Mus'ab overpowered him. He lost all control over himself and asked: "How can one become a Muslim?" They replied: "Confess the Oneness of Allah, wash your body and dress with water and offer prayers".
Usayd, who had come to shed the blood of these two persons, acknowledged with an open mind, the Oneness of Allah and the prophethood of the Prophet. He took bath, washed his dress and then returned to Sa'd, humming the 'Shahadatain' (Acknowledgement of the Oneness of Allah and Prophethood of Muhammad) Sa'd bin Ma'az was waiting for him very anxiously.
Suddenly Usayd appeared with a happy and glowing face. Sa'd bin Ma'az turned to those present and said: "By Allah! Usayd has changed his faith and has not achieved the object for which he went". Usayd came up and explained the matter. Sa'd bin Ma'az got up in extreme anger so as to check the two persons from propagating Islam and shed their blood.
However, the same thing, which had happened to Usayd, happened to him. He too had to surrender before the strong logic and the attractive and sweet words of Mus'ab. Signs of remorse appeared on his face for what he had decided upon, and now he declared his allegiance to Islam. He bathed then and there and purified his clothes.
Thereafter he turned to his people and said to them: "What position do I enjoy amongst you?" They replied: "You are the head and chief of our tribe". Then he said: "I shall not speak with any man or woman of my tribe unless they embrace Islam".
The words of the chief were passed on from mouth to mouth to all the members of the tribe and within a short time and before even seeing the Prophet the entire tribe of Bani Abdul Ashhal embraced Islam and became defenders of this sacred religion