In the early days of Islam, Najran was a large center of people who had changed from idol worship to Christianity. The Holy Prophet (s.a.w) had sent letters to the heads of different countries inviting them to Islam. One such letter was addressed to the Christians of Najran. It read as follows: "In the Name of the God of Ibrahim, Ishaaq and Ya'qub.
This letter is from Muhammad, the Prophet and Messenger of Allah to the Asqaf (Bishop) of Najran.
Praise be to the God of Ibrahim, Ishaaq and Ya'qub. I invite you to worship Allah instead of (His) servants. I invite you to come out of the rule of the servants of Allah and into the rule of Allah Himself. If you do not accept my invitation, then you should (at least) pay Jizya (tax) to the Islamic State (so that your lives and properties may be protected), otherwise you are warned of a danger."
By using the names of the ancient Prophets (a.s), the Holy Prophet (s.a.w) wanted to let the Christians of Najran know that the belief in One God he was teaching was the same as that preached by the previous Prophets Ibrahim, Ishaaq and Ya'qub (a.s), in whom they also believed. It is also mentioned that the Holy Prophet (s.a.w) included the following verse of the Holy Qur'an in the letter:
"Say, (O Muhammad), "O people of the Book (Bible), come to an agreement between us and you; that we shall worship none but Allah, and that we shall claim no partner to Him, and that none of us shall take others for lords besides Allah." And if they turn away, then say, "Bear witness that we are Muslims (those who have surrendered to Allah)". (Quran 3:6)
When this message was delivered to Abu Haris, who was the Asqaf and leader of the Church, he read it carefully and then appointed a committee of some religious and wise people to decide on the matter.
One of them, who was an experienced and intelligent person, advised that a group representing the people of Najran should go to Madina to study the claim of Prophethood by the Holy Prophet (s.a.w).
60 people, considered to be the most wise and knowledgeable from the people of Najran, were elected. They were led by three of their religious men. The group arrived in Madina to the Holy Prophet (s.a.w) who received them with a warm welcome. Before they entered into a discussion, they requested for permission to say their prayers and this was granted. They were put in one part of the mosque where they could pray with ease and comfort. Then the following conversation took place:
The Holy Prophet (s.a.w):
I invite you towards the belief of Tawhid and the worship of One God and submission to His will. (Then he recited verse 64 of Surah Aalay Imran.)

Christians Fathers:
If Islam means faith in the One God of the Universe, we already believe in Him and follow His Commands.
The Holy Prophet (s.a.w):
Islam has a few signs and some of your actions show that you have not accepted true Islam. How do you claim worship of One God when you worship the cross and do not abstain from eating pork and believe that God has a son?

A Christian Father:
Certainly he [Isa (a.s)] was the son of God because his mother Mary [Maryam (a.s)] had given birth to him without marrying anyone in this world. Therefore obviously his father is the God of this Universe. We also believe in Jesus [Isa (a.s)] as God because he used to bring the dead back to life, cure the sick and create birds from clay and make them fly. All this points to the fact that he is God.
The Holy Prophet (s.a.w):
No, he was the servant and creature of God… All his power and strength was granted to him by God.
At this time, angel Jibraeel (a.s) brought the following verse of the Holy Qur'an from Allah:
"Surely the example of Isa to Allah is like that of Adam; He created him from dust, and then said to him, 'Be!' and he was". (Quran 3:59)
This meant that if Isa (a.s) could be called the son of God because of the fact he was born without a father, then Adam (a.s) deserved this title more, because he was born without a father and mother. The Christian Fathers could not reply to this argument but they continued to argue out of obstinacy. Then the following verse of the Holy Qur'an was revealed:
"And whoever argues with you in this matter after what has come to you of knowledge, then say, "COME, LET US CALL OUR SONS AND YOUR SONS AND OUR WOMEN AND YOUR WOMEN AND OURSELVES AND YOURELVES , THEN LET US HUMBLY PRAY ( TO OUR LORD ) AND INVOKE THE CURSE OF ALLAH UPON THE LIARS".
(Quran 3:61)
The Holy Prophet (s.a.w) produced this verse before the Christians and declared the challenge of "Mubahila", which means to curse one another. The Christians consulted each other and announced their acceptance of the challenge. Then they returned to their camp.
It was agreed between the two parties that the contest would take place the next day in the open desert outside the city of Madina. On the 24th of Zilhaj 10 A.H, the Holy Prophet (s.a.w) came out for Mubahila. He held Imam Husain (a.s) in his arms and he held Imam Hasan (A) by his hand. sayyedah Fatima (s.a) came behind him, while behind her came Imam Ali (a.s). The Holy Prophet (s.a.w) said to them, "when I pray you should say Ameen."
In obedience to the verse of Mubahila sent by Allah , the Holy Prophet (s.a.w) had brought Imam Hasan (a.s) and Imam Husain (a.s) as his "SONS", hazrat Fatima (a.s) as his "WOMEN" and Imam Ali (a.s) as his "SELF".
The Christian Fathers, on seeing the beautiful and shining faces in front of them became spellbound. Their hearts trembled and they began to shake on seeing the power radiating from Ahlul Bayt (a.s). Their leader asked someone, "who are these persons, who have come with Muhammad?" The man told him the names and their relationship with the Holy Prophet (s.a.w).
He could hold his patience no longer and he cried out, "by God, I am seeing such faces that if they were to pray to God to move the mountain, God Almighty would move the mountain for them.”
Oh you people of Najran, if you contest with Muhammad in this prayer of invoking curses on the liars, then I warn you that all of you will be destroyed and not a single soul will remain on this earth. I feel that it would be better to surrender to them and obey them."
When the Holy Prophet (s.a.w) heard these words he remarked, "By God, had the Christians of Najran contested with us, they would have been transformed into monkeys and swines. Fire would have rained over them."
When the Christian Fathers backed away from Mubahila, the Holy Prophet (s.a.w) gave them two choices; either to accept Islam or agree to come to terms.
The Christians would not agree to accept Islam and therefore a treaty was signed on the following terms:
- Every year, the Christians of Najran would give to the Islamic Government two thousand pieces of clothing, the cost of which would be forty dirhams each.
- They would also provide 30 horses, 30 camels, 30 battle armours and 30 spears, temporarily to the Muslim army, if the Holy Prophet (s.a.w) needed these in any war.
The treaty was dictated by the Holy Prophet (s.a.w), written by Imam Ali (a.s) and had the signatures of four companions of the Holy Prophet (s.a.w) as witnesses.
One of the important conditions agreed in this treaty was that the people of Najran would not deal in usury (interest taking) of any sort, otherwise the Holy Prophet (s.a.w) would not remain bound by the treaty with them.
After the Christian returned home, a few respectable persons from Najran came to Madina and willingly accepted Islam and became true Muslims.