Around 9 A.H, a delegation of clerics travelled from Najran to Medina. They expressed that while they submitted to the political power of the Prophet, they did not want to convert to Islam because they saw themselves as possessing the true religion.
The Quran verses 3:59-61
The likeness of Jesus in God’s sight is that of Adam: He created him from dust, then said to him, “Be,” and he was.
are said to be related to this event, Ibn-Kathir on 3:61 (English translation):
The reason for the call to Mubahalah and the revelation of the Ayat from the beginning of this Surah until here, is that a delegation from the Christians of Najran (in Yemen) came to Al-Madinah to argue about 'Isa, claiming that he was divine and the son of Allah. Allah sent down the beginning of this Surah until here, to refute their claims, as Imam Muhammad bin Ishaq bin Yasar and other scholars stated.
Muhammad bin Ishaq bin Yasar said in his famous Sirah, "The delegation of Christians from Najran came to the Messenger of Allah . The delegation consisted of sixty horsemen, including fourteen of their chiefs who make decisions. These men were Al-'Aqib, also known as 'Abdul-Masih, As-Sayyid, also known as Al-Ayham, Abu Harithah bin 'Alqamah, of ﴿the family of﴾ Bakr bin Wa'il and Uways bin Al-Harith. They also included, Zayd, Qays, Yazid, Nabih, Khuwaylid, 'Amr, Khalid, 'Abdullah and Yuhannas. Three of these men were chiefs of this delegation, Al-'Aqib, their leader and to whom they referred for advice and decision; As-Sayyid, their scholar and leader in journeys and social gatherings; and Abu Harithah bin 'Alqamah, their patriarch, priest and religious leader. Abu Harithah was an Arab man from ﴿the family of﴾ Bakr bin Wa'il, but when he embraced Christianity, the Romans and their kings honored him and built churches for him (or in his honor). They also supported him financially and gave him servants, because they knew how firm his faith in their religion was.'' Abu Harithah knew the description of the Messenger of Allah from what he read in earlier divine Books. However, his otherwise ignorance led him to insist on remaining a Christian, because he was honored and had a high position with the Christians. Ibn Ishaq said, "Muhammad bin Ja'far bin Az-Zubayr said that, "The (Najran) delegation came to the Messenger of Allah in Al-Madinah, entered his Masjid wearing robes and garments, after the Prophet had prayed the 'Asr prayer. They accompanied a caravan of camels led by Bani Al-Harith bin Ka'b. The Companions of the Messenger of Allah who saw them said that they never saw a delegation like them after that... Then Abu Harithah bin 'Alqamah and Al-'Aqib 'Abdul-Masih or As-Sayyid Al-Ayham spoke to the Messenger of Allah , and they were Christians like the king (Roman King). However, they disagreed about 'Isa; some of them said,'He is Allah,' while some said, 'He is the son of Allah,' and some others said, 'He is one of a trinity.' Allah is far from what they attribute to Him.''
Indeed, these are the creeds of the Christians. They claim that 'Isa is God, since he brought the dead back to life, healed blindness, leprosy and various illnesses, told about matters of the future, created the shape of birds and blew life into them, bringing them to life. However, all these miracles occurred by Allah's leave, so that 'Isa would be a sign from Allah for people.
They also claim that 'Isa is the son of Allah, since he did not have a father and he spoke when he was in the cradle, a miracle which had not occurred by any among the Children of Adam before him, so they claim. They also claim that 'Isa is one of a trinity, because Allah would say, 'We did, command, create and demand.' They said, 'If Allah were one, he would have said, "I did, command, create and decide." This is why they claim that 'Isa and Allah are one (Trinity). Allah is far from what they attribute to Him, and we should mention that the Qur'an refuted all these false Christian claims.
Ibn Ishaq continued, "When these Ayat came to the Messenger from Allah , thus judging between him and the People of the Book, Allah also commanded the Prophet to call them to the Mubahalah if they still refused the truth. The Prophet called them to the Mubahalah. They said, 'O Abu Al-Qasim! Let us think about this matter and get back to you with our decision to what we want to do.' They left the Prophet and conferred with Al-'Aqib, to whom they referred to for advice. They said to him, 'O 'Abdul-Masih! What is your advice' He said, 'By Allah, O Christian fellows! You know that Muhammad is a Messenger and that he brought you the final word regarding your fellow ('Isa). You also know that no Prophet conducted Mubahalah with any people, and the old persons among them remained safe and the young people grew up. Indeed, it will be the end of you if you do it. If you have already decided that you will remain in your religion and your creed regarding your fellow ('Isa), then conduct a treaty with the man (Muhammad) and go back to your land.' They came to the Prophet and said, 'O Abu Al-Qasim! We decided that we cannot do Mubahalah with you and that you remain on your religion, while we remain on our religion. However, send with us a man from your Companions whom you are pleased with to judge between us regarding our monetary disputes, for you are acceptable to us in this regard.'''
Al-Bukhari recorded that Hudhayfah said, "Al-'Aqib and As-Sayyid, two leaders from Najran, came to the Messenger of Allah seeking to invoke Allah for curses (against whoever is unjust among them), and one of them said to the other, 'Let us not do that. By Allah, if he were truly a Prophet and we invoke Allah for curses, we and our offspring shall never succeed afterwards.' So they said, 'We will give you what you asked and send a trusted man with us, just a trusted man.' The Messenger of Allah said;
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Finally, it was agreed that the people of Najran should pay the Prophet an annual tribute of 2,000 pieces of clothing, in return for which the Prophet assured them protection for life and religion. The treaty on this, narrated in the Siyar of al-Shaibānī and various works, was renewed under the Caliphs Abu Bakr and Umar ibn al-Chattab (source of the first and the last paragraph: Wikipedia.de citing from Majid Khadduri: The Islamic Law of Nations: Shaybānī's Siyar. Baltimore: The Johns Hopkins Press 1966. S. 278–280).