The young Muadh became a Muslim at the hands of Musab ibn Umayr, the daiy (missionary) whom the Prophet had sent to Yathrib before the hijrah. Muadh was among the seventy-two Yathribites who journeyed to Makkah, one year before the hijrah, and met the Prophet at his house and later again in the valley of Mina, outside Makkah, at Aqabah. Here the famous second Aqabah Pledge was made at which the new Muslims of Yathrib, including some women, vowed to support and defend the Prophet at any cost. Muadh was among those who enthusiastically clasped the hands of the blessed Prophet then and pledged allegiance to him.
As soon as Muadh returned to Madinah from Makkah, he and a few others of his age formed a group to remove and destroy idols from the houses of the mushrikeen in Yathrib. One of the effects of this campaign was that a prominent man of the city, Amr ibn al-Jumuh, became a Muslim.
When the noble Prophet reached Madinah, Muadh ibn Jabal stayed in his company as much as possible. He studied the Quran and the laws of Islam until he became one of the most well-versed of all the companions in the religion of Islam.
Wherever Muadh went, people would refer to him for legal judgments on matters over which they differed. This is not strange since he was brought up in the school of the Prophet himself and learnt as much as he could from him. He was the best pupil of the best teacher. His knowledge bore the stamp of authenticity. The best certificate that he could have received came from the Prophet himself when he said: "The most knowledgeable of my ummah in matters of Halal and haram is Muadh ibn Jabal."
One of the greatest of Muadhs contributions to the ummah of Muhammad was that he was one of the group of six who collected the Quran during the lifetime of the Prophet, peace be upon him. Whenever a group of companions met and Muadh was among them, they would look at him with awe and respect on account of his knowledge. The Prophet and his two Khalitahs after him placed this unique gift and power in the service of Islam .
After the liberation of Makkah, the Quraysh became Muslims en masse. The Prophet immediately saw the need of the new Muslims for teachers to instruct them in the fundamentals of Islam and to make them truly understand the spirit and letter of its laws. He appointed Attab ibn Usay as his deputy in Makkah and he asked Muadh ibn Jabal to stay with him and teach people the Quran and instruct them in the religion.
Sometime after the Prophet had returned to Madinah, messengers of the kings of Yemen came to him announcing that they and the people of Yemen had become Muslims. They requested that some teachers should be with them to teach Islam to the people. For this task the Prophet commissioned a group of competent duat (missionaries) and made Muadh ibn Jabal their amir. He then put the following question to Muadh:
"According to what will you judge?"
"According to the Book of God," replied Muadh.
"And if you find nothing therein?"
"According to the Sunnah of the Prophet of God."
"And if you find nothing therein?"
"Then I will exert myself (exercise ijtihad) to form my own judgment."
The Prophet was pleased with this reply and said: "Praise be to God Who has guided the messenger of the Prophet to that which pleases the Prophet."
The Prophet personally bade farewell to this mission of guidance and light and walked for some distance alongside Muadh as he rode out of the city. Finally he said to him:
"O Muadh, perhaps you shall not meet me again after this year. Perhaps when you return you shall see only my mosque and my grave." Muadh wept. Those with him wept too. A feeling of sadness and desolation overtook him as he parted from his beloved Prophet, peace and blessings of God be on him.
The Prophet's premonition was correct. The eyes of Muadh never beheld the Prophet after that moment. The Prophet died before Muadh returned from the Yemen. There is no doubt that Muadh wept when he returned to Madinah and found there was no longer the blessed company of the Prophet.
During the caliphate of Umar, Muadh was sent to the Banu Kilab to apportion their stipends and to distribute the sadaqah of their richer folk among the poor. When he had done his duty, he returned to his wife with his saddle blanket around his neck, empty handed, and she asked him:
"Where are the gifts which commissioners return with for their families?" "I had an alert Supervisor who was checking over me," he replied. "You were a trusted person with the messenger of God and with Abu Bakr. Then Umar came and he sent a supervisor with you to check on you!' she exclaimed. She went on to talk about this to the women of Umar's household and complained to them about it. The complaint eventually reached Umar, so he summoned Muadh and said:
"Did I send a supervisor with you to check on you?"
"No, Amir al-Mumineen," he said, "But that was the only reason I could find to give her." Umar laughed and then gave him a gift, saying, "I hope this pleases you."
Also during the caliphate of Umar, the governor of Syria, Yazid ibn Abi Sufyan sent a message saying:
"O Amir al-Mumineen! The people of Syria are many. They fill the towns. They need people to teach them the Quran and instruct them in the religion."
Umar thereupon summoned five persons who had collected the Quran in the lifetime of the Prophet, peace be upon him. They were Muadh ibn Jabal, Ubadah ibn asSamit, Abu Ayyub al-Ansari, Ubayy ibn Kab and Abu adDardaa. He said to them:
"Your brothers in Syria have asked me to help them by sending those who can teach them the Quran and instruct them in the religion. Please appoint three among you for this task and may God bless you. I can select three of you myself if you do not want to put the matter to the vote."
"Why should we vote?" they asked. "Abu Ayyub is quite old and Ubayy is a sick man. That leaves three of us." "All three of you go to Homs first of all. If you are satisfied with the condition of the people there, one of you should stay there, another should go to Damascus and the other to Palestine."
So it was that Ubadah ibn as-Samit was left at Homs, Abu ad-Dardaa went to Damascus and Muadh went to Palestine. There Muadh fell ill with an infectious disease. As he was near to death, he turned in the direction of the Kabah and repeated this refrain: "Welcome Death, Welcome. A visitor has come after a long absence . . ." And looking up to heaven, he said: "O Lord, You know that I did not desire the world and to prolong my stay in it . . . O Lord, accept my soul with goodness as you would accept a believing soul..."
He then passed away, far from his family and his clan, a daiy in
the service of God and a muhajir in His path.