Tafsir Ibn Abbas: Aal-i-Imraan, Ayah 61

And whoever from among the Christians disputes with you concerning him after the knowledge of his affair that has come to you say to them ‘Come! Let us call our sons and your sons our wives and your wives our selves and your selves and gather them together then let us humbly pray and invoke God’s curse upon those who lie’ by saying ‘Lord curse the one that tells lies concerning the affair of Jesus’. The Prophet s had called upon the Najrān delegation to do this when they disputed with him about Jesus. They said ‘Let us think about it and we will come back to you’. The judicious one among them said ‘You know that he is a prophet and that every people that has ever challenged a prophet to a mutual imprecation has been destroyed’. They left him and departed. When they went to see the Prophet s who had set out with al-Hasan al-Husayn Fātima and ‘Alī he said to them the Najrān delegation ‘When I supplicate you say ‘Amen’; but they refrained from this mutual imprecation and made peace with the Prophet on the condition that they pay the jizya as reported by Abū Nu‘aym. According to Ibn ‘Abbās the Prophet said ‘Had they set out and performed the mutual cursing they would have gone home and found neither possessions nor family’. It is also reported that had they set out with this intention they would have been consumed by fire.