The leaders and scholars of the Christians of Najran gathered to discuss the letter sent to them by the Prophet (peace and blessings of Allah be upon him and his family), in which he invited them to Islam. They were unable to reach a definitive conclusion, as they possessed teachings confirming the coming of a prophet after Jesus (peace be upon him), and the signs that had appeared in Muhammad indicated his prophethood.

Therefore, they decided to send a delegation to meet the Prophet (peace and blessings of Allah be upon him and his family) and engage him in discussion.

The Prophet (peace and blessings of Allah be upon him and his family) received the large delegation. At first, he appeared displeased with their appearance, which bore signs of their religious customs, as they were wearing brocade and silk, wearing gold, and carrying crosses around their necks. They came to him again later after changing their appearance, whereupon he welcomed them, treated them with respect, and gave them permission to perform their religious rituals.

He then presented Islam to them and recited verses from the Qur’an to them, but they refused to accept it, and the debate with them became prolonged. Eventually, they agreed that the Prophet (peace and blessings of Allah be upon him and his family) would engage in Mubahalah with them. This was by the command of Allah, the Almighty, and they agreed to meet on the following day.

The Messenger of Allah (peace and blessings of Allah be upon him and his family) went out to meet them carrying al-Husayn, while holding al-Hasan by the hand, and behind him were his daughter Fatimah and his cousin Ali ibn Abi Talib. This was in obedience to the command of Allah, the Exalted, as stated in the Holy Qur’an:

“Then whoever argues with you concerning it after the knowledge that has come to you, say: ‘Come, let us call our sons and your sons, our women and your women, ourselves and yourselves; then let us earnestly pray and invoke the curse of Allah upon those who are lying.’”
(Qur’an 3:61)

He did not take anyone else from among the Muslims with him, demonstrating the truthfulness of his prophethood and his message. At this point, the Bishop of Najran said:

“O Christians, I see faces which, if they were to ask Allah to move a mountain from its place, He would surely move it. Therefore, do not engage in Mubahalah with them, lest you perish, and no Christian would remain on the face of the earth.”

When they refused to engage in Mubahalah with the Prophet and his Ahl al-Bayt (peace and blessings of Allah be upon them all), the Messenger said to them:

“Since you have refused Mubahalah, then accept Islam. You will have what the Muslims have, and upon you will be what is upon the Muslims.”

They refused. He then said:

“Then I shall fight you.”

They replied:

“We have no strength to fight the Arabs, but we will make peace with you on the condition that you do not attack us and do not turn us away from our religion, and that we pay you two thousand garments every year: one thousand in Safar and one thousand in Rajab, as well as thirty ordinary iron coats of armor.”

The Prophet made peace with them on those terms and said:

“By Him in Whose hand is my soul, destruction had already drawn near to the people of Najran. Had they engaged in Mubahalah, they would have been transformed into monkeys and pigs, the valley would have been set ablaze around them, and Najran and its people would have been completely destroyed, even the birds in the trees. The year would not have passed before all the Christians perished.”

They therefore returned to their homeland without accepting Islam.

It is also narrated that al-Sayyid and al-‘Aqib, two of their leaders, did not remain away for long before returning to the Prophet (peace and blessings of Allah be upon him and his family) to declare their acceptance of Islam.

If you want, I can also translate the next Arabic passage in the same formal style.