…then let us humbly pray (nabtahil)
That is, 'Let us invoke [God's] curse, one upon the other.' The one who beseeches (mubtahil) is the supplicant (dā'ī), and the [act of] beseeching (ibtihāl) is supplication (du'ā'). The one who glorifies (musabbiḥ) is the one who remembers (dhākir), and this is not written down by the recording angels, for it is the witnessing of the One remembered in a remembrance that is through the One remembered. This is the meaning of His saying (ḥadīth qudsī), 'I keep company with the one who remembers Me, and when and wherever My servant seeks me out he will find Me.'
Tanwîr al-Miqbâs min Tafsîr Ibn ‘Abbâs :
Allah then mentioned the dispute of the delegation of Najran with the Prophet (pbuh) after he explained to them that the likeness of Jesus with Allah is as the likeness of Adam, for they said to the Prophet: it is not as you say that Jesus was not Allah, his son or His partner. As response Allah said: (And whoso disputeth with thee concerning him) concerning Jesus, (after the knowledge which has come unto thee) after the exposition that has come to you that Jesus was not Allah, His son or His partner, (say (unto him): Come! We will summon our sons and your sons) and you summon your sons, (and our women and your women) and you summon your women, (and ourselves and yourselves, then we will pray humbly (to our Lord)) and exert our effort in praying ((and (solemnly) invoke) all together (the curse of Allah upon those who lie) about Allah concerning Jesus.
Asbab Al-Nuzul by Al-Wahidi :
(… say (unto him): Come! We will summon our sons and your sons…) [3:61]. Abu Sa‘d informed us> ‘Abd al-Rahman ibn Muhammad al-Zimjari> Ahmad ibn Ja‘far ibn Malik> ‘Abd Allah ibn Ahmad ibn Hanbal> his father> Husayn> Hammad ibn Salamah> Yunus> al-Hasan who said: “The two monks of Najran came to see the Prophet, Allah bless him and give him peace, and he invited them to surrender to Allah. One of them said: ‘We have surrendered to Allah before you’. He said: ‘You lie! Three things prevent you from surrendering to Allah: your prostration before the cross, your claim that Allah has a son and your consumption of wine’. They said: ‘What do you say about Jesus?’ The Prophet, Allah bless him and give him peace, did not answer. But then this verse was revealed (This (which) We recite unto thee is a revelation and a wise reminder… Lo! the likeness of Jesus with Allah is as the likeness of Adam) up to Allah’s saying (… say (unto him): Come! We will summon our sons and your sons…). Then the Messenger of Allah, Allah bless him and give him peace, challenged them to summon Allah’s curse upon the one who is lying amongst them (Mula‘anah). The Messenger of Allah, Allah bless him and give him peace, went and brought al-Hasan, al-Husayn, Fatimah and all his family and children, peace be upon them. When the two Christians left, one of them said to the other: ‘Consent to pay the Jizyah and do not agree to summon Allah’s curse on the liar’. They went back and said: ‘We agree to pay the Jizyah and abstain from summoning Allah’s curse on the liar’ ”. ‘Abd al-Rahman ibn al-Hasan al-Hafiz informed us among that which he gave us permission to narrate from him> Abu Hafs ‘Umar ibn Ahmad al-Wa‘iz> ‘Abd Allah ibn Sulayman ibn al-Ash‘ath> Yahya ibn Hatim al-‘Askari> Bishr ibn Mihran> Muhammad ibn Dinar> Dawud ibn Abi Hind> al-Sha‘bi> Jabir ibn ‘Abd Allah who said: “The delegation of the people of Najran came to see the prophet, Allah bless him and give him peace. The deputy chief and the master spoke with the Prophet and he invited them to surrender to Allah. They said: ‘We have surrendered to Him before you’. He said: ‘You lie! And if you wish I will inform you about that which prevents you from surrendering to Allah’.
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