Final answer:
The Christians of Najran came for Mubahala with Prophet Muhammad (S), but backed out possibly due to the fear of potential divine wrath if they were in the wrong.
Step-by-step explanation:
The event referred to in the question is the Mubahala, which happened between Prophet Muhammad (S) and the Christians of Najran. The Mubahala was a mutual prayer contest in which the Prophet's opponents would request God's curse upon the liars. It's stated in the Qur'an and occurred as a result of a theological discussion between Prophet Muhammad (S) and the Christians of Najran.
When the Prophet (S) asked them to partake in the Mubahala, the Christians of Najran withdrew from it. It is believed that they declined because they were not fully confident in their claims and feared God's punishment if they were exposing themselves to His curse falsely. As a result, no Mubahala actually took place.
Learn more about Mubahala