When the people of the first pledge of al-‘Aqabah returned to Madinah and Islam spread to every single household among the Ansar, they sent a man to the Messenger of Allah (pbuh) with a letter asking him to send them someone who would teach them the Deen and the Qur’an. The Messenger of Allah (pbuh) never used to leave those who embraced Islam without teaching them the rules and nurturing them with the sound Islamic culture which would enable them to understand Islam and realize its essence. For the Islamic culture is vital to every Muslim, and is a means of strengthening the ‘Aqeedah and of understanding the Message of Islam, and thereby guarantees the consistent application of Islam. Those who embraced Islam had sensed this, therefore, they asked for someone to teach them, and the Messenger of Allah (pbuh) sent Mus’ab ibn ‘Umayr to them.
On arrival, Mus’ab lodged with As’ad ibn Zurarah, he then began visiting people in their homes and camps, calling them to Islam and reciting the Qur’an and consequently a man or two would embrace Islam, until Islam manifested itself and spread to every household of the Ansar, except the households of Khatmah, Wa’il and Waqif who were from (the clan of) Aws-Allah. Mus’ab ibn ‘Umayr was teaching them the deen and recitation of the Qur’an. Then he wrote to the Messenger of Allah (pbuh) asking his permission to gather them. Allah’s Messenger (pbuh) granted him permission and wrote back, “Wait until the Jews declare their Sabbath, and in the afternoon, approach Allah with two Rak’at and then deliver your Khutbah.” Mus’ab ibn ‘Umayr gathered them in the house of Sa’d ibn Khaythamah, they were twelve men and he slaughtered for them one goat. Mus’ab was the first in the history of Islam to hold Jum’uah prayer.
Mus’ab continued to go around Madinah calling people to Islam and teaching them the Deen.
One day As’ad ibn Zurarah went out with Mus’ab ibn ‘Umayr to the areas of Banu al-Ashhal and of Banu Zafar (Sa’d ibn Mu’adh was incidentally As’ad ibn Zurarah’s maternal cousin.) They entered one of the gardens of Banu Zafar by a well called Maraq and sat in it, where some of the men who had accepted Islam had gathered together. Sa’d ibn Mu’adh and Usayd ibn Hudayr were at the time leaders of their clan, the Banu ‘Abd al-Ashhal, and both followed the polytheism of their tribe. When they had heard about Mus’ab, Sa’d said to Usayd, “Go to these fellows who have entered our quarters to make fools of our comrades, drive them out and forbid them to enter our quarters.
If it were not that As’ad ibn Zurarah is related to me as you know I would save you the trouble. He is my aunt’s son and I can do nothing to him.” So Usayd took his lance and went to them; and when As’ad saw him he said to Mus’ab, “This is the chief of his tribe who is coming to you, so be true to Allah with him.” Mus’ab said, “If he will sit down, I will talk to him.” He stood over them looking furious and asking what they meant by coming to deceive their weaker comrades. “Leave us if you value your lives.” Mus’ab said, “Won’t you sit down and listen. If you like what you hear you can accept it, and if you don’t like it you can leave it alone.” He agreed that was fair, stuck his lance in the ground, and sat down. Mus’ab explained Islam to him and read the Qur’an. Afterwards they said, according to what has been reported by them, “By Allah, before he spoke we recognized Islam in his face by its peaceful glow.” He said, “What a wonderful and beautiful discourse this is! What does one do if he wants to enter this Deen?” They told him that he must wash and purify himself and his garments, then bear witness to the Truth and pray two Rak’at. He immediately did so and said, “There is a man behind me who if he follows you every one of his people will follow suit. I will send him to you at once. It is Sa’d ibn Mu’adh.”
Taking his lance, he went off to Sa’d and his people sitting in a meeting place. When Sa’d saw him coming, he said, “By Allah, Usayd is coming with a different expression from that which he had when he left you.” And when he came up he asked what had happened, he said, “I have spoken to the two men and I find no harm in them. I forbade them to go on and they said to me: We will do what you like; and I was told that Banu Harithah had gone out against As’ad to kill him because they knew that he was the son of your aunt so as to make you appear a treacherous protector of your guests.”
Sa’d was enraged and got up at once, alarmed at what had been said about the Banu Harithah. He took the lance from his hand saying, “By Allah (swt) see that you have been utterly ineffective.” He went out to them and when he saw them sitting comfortably he knew that Usayd had intended that he should listen to them. He stood over them, looking furious. He said to As’ad, “O Abu Umamah, were it not for the relationship between us you would not have treated me thus. Would you behave in our homelands in a way we detest?” As’ad already had said to Mus’ab, “O Mus’ab, by Allah the leader who is followed by his people has come to you. If he follows you, no two of them will remain behind.” So Mus’ab said to him, “Won’t you sit down and listen. If you like what you hear you can accept it, and if you don’t like it you can leave it alone.” He agreed that was fair, stuck his lance in the ground, and sat down. He explained Islam to him and read for him the Qur’an.
Afterwards they said, according to what has been reported of them, “By Allah, before he spoke we recognized Islam in his face by its peaceful glow.” He said, “What a wonderful and beautiful discourse this is! What does one do if he wants to enter this Deen?” They told him that he must wash and purify himself and his garments, then bear witness to the truth and pray. He immediately did so. Then he took his lance and went back to his people’s meeting place accompanied by Usayd ibn Hudayr. When they saw him coming they said, “We swear by Allah, Sa’d has returned with a different expression from that which he had when he left you.” And when he stopped by them he said, “O Banu ‘Abd al-Ashhal, how do you rate my authority amongst you?” They replied, “You are our chief, the most active in our interests, the best in judgment and the most fortunate in leadership.” He said, “I will not speak to a man or woman among you until you believe in Allah and his Messenger.” As a result, every man and woman among the Banu ‘Abd al-Ashhal embraced Islam. Mus’ab then returned to the house of As’ad ibn Zurarah and he stayed with him as a guest, and he continued to call the people to Islam until almost every household of the Ansar had Muslim men and women among them. Mus’ab ibn ‘Umayr remained in Madinah for one year among the ‘Aus and the Khazraj teaching them their Deen and witnessing, with great delight, the growing number of the helpers of Allah’s authority and of the word of truth.
He, may Allah be pleased with him, used to knock on people’s doors hoping to contact them and convey the Message of Allah. He used to walk to the fields and contact the farmers to call them to Islam. He also used to confront the leaders and call them to the Deen of Allah. He would also perform some deliberate tactics like the one he used with As’ad ibn Zurarah in order to gain access to people and get them to receive the voice of Truth until he managed in one single year to turn the thoughts in Madinah from corrupted idolatry and incorrect emotions to Tawheed and Iman and Islamic emotions that abhorred Shirk and turned away from evil acts such as cheating and fraud and other vices. As a result of Mus’ab’s activities and the activities of those who embraced Islam, Madinah had been transformed in one single year from a people who committed Shirk to a people who turned to Islam.