As Salaam Alaykum, Ibn Abbas has reported that a deputation of the Christians of Najran along with seven priests visited the Holy Prophet (Sallalaahu Alayhi wa Sallam), and they said: "O Muhammad, tell us what is your Lord like and of what substance He is made."The Holy Prophet (Sallalaahu Alayhi wa Sallam) replied: "My Lord is not made from any substance: He is unique and exalted above everything."Thereupon Allah sent down this Surah (Al-Ikhlaas). I would like to know for whether this Hadeeth is authentic and if so can one use or send this Hadeeth to Christian friends to do Dawah? Shukran.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

We have not come across this Hadeeth in the reliable books of Hadeeth and Sunnah. However, it was mentioned by Ar-Raazi in “At-Tafseer Al-Kabeer” from the narration of ‘Attaa’ from Ibn ‘Abbaas but he did not attribute it to any book of the books of Sunnah.

However, the reason of revelation of Chapter Al-Ikhlaas [Quran 112] that is mentioned in Fatwa 132411 is enough for you, therefore, you may send it to them as it serves the objective which is the call to Tawheed [the Oneness of Allaah].

It should be noted that it is not permissible for a Muslim to be friendly with non-Muslims as Allaah Says (what means): {O you who have believed, do not take My enemies and your enemies as allies, extending to them affection while they have disbelieved in what came to you of the truth.}[Quran 60:1] However, it is permissible to be kind to them as Allaah clarified in His Book. Allaah Says (what means): {Allaah does not Forbid you from those who do not fight you because of religion and do not expel you from your homes - from being righteous toward them and acting justly toward them. Indeed, Allaah loves those who act justly.}[Quran 60:8] 

Of course, among the best acts of being kind to them is to call them to Islam; for more benefit, please refer to Fatwa 88293.

Allaah Knows best.