The author of Kashaf, although a very biased person, records in detail the event of Mubahila. When the Prophet (S) invited the Christians of Najran for Mubahila (mutual imprecation to prove one’s point), the Christians requested for some time that they wanted to discuss the matter with their Bishop. The Bishop said that Muhammad (S) was truly the Prophet and he has presented the truth in front of you. Whosoever takes recourse to an imprecation with a Prophet gets destroyed. If you take any such step, it will be calamitous for your community. If you wish to safeguard your community then go and seek for a truce.
On the morning of the appointed day the Prophet (S) came out for the purpose of Mubahila with Imam Husayn (as) in his arms, Imam Hasan (as) holding the finger of his right hand and behind him followed Fatima and ‘Ali (as). Thus arrived the small group into the selected ground and the Prophet (S) told to the four Immaculates with him that the moment he uttered the prayer against the opponents, all the four of them should say, “Aameen!” On the other side, when the Bishop of Najran saw this scene, he told to his people, “O group of Christians! I see in front of me such faces that if they pray, the mountain will move from its place! Don’t enter into an imprecation with them, otherwise there will not remain a single Christian on the Earth!”
Therefore, all those persons came to the presence of the Prophet (S) and told him that they decided not to have an imprecation with them.
The Prophet (S) then said, “If you don’t wish to have an imprecation as per our previous agreement, then you accept Islam.”
The Christians refused to accept this suggestion.
Then the Prophet (S) said, “In this event, prepare for a battle!”
They said, “we do not have the strength to battle with you and we want a truce.”
Therefore the truce was made on the condition that every year two thousand Hillas were to be given in the month of Safr and one thousand in the month of Rajab, thirty high quality chains of arm to also be given every year. After the truce the Prophet (S) told them that if the Christians had not entered into this agreement and opted for the imprecation, no single person of the group would have lived. Even the birds on the trees of the forest would have perished and the entire community of Christians would have perished within the period of one year.