What is the origin of the incorrect Christian belief that ‘Eesaa, may Allaah exalt his mention, is the son of Allaah? How can we refute this allegation?

All perfect praise is for Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.

The Christians introduced illogical ideas into their creed that no sound mind can accept.  Among these is their belief that ‘Eesaa is the son of Allaah. The reason behind this incorrect belief is that his was a virgin birth - without a father - and that the innocence and purity of his mother, Maryam (Mary), may Allaah exalt her mention, has been decisively proven. Among these proofs is that ‘Eesaa spoke from his cradle informing his people about the innocence of his mother. 

It seems therefore that when the Christians did not identify his father and received divine texts describing him as "the word of Allaah" and "the spirit of Allaah", they attributed him to Allaah as His son; Exalted is Allaah and far above what they claim by great sublimity.

Refuting them is quite easy. If we accept that Allaah the Almighty created Aadam (Adam) without a father or a mother, and that He created Hawwaa’ (Eve) likewise, then why should they find it strange that He created ‘Eesaa without a father?

Calling Him ‘the Word of Allaah’ simply means that ‘Eesaa was created and formed by virtue of the command of Allaah Almighty when He said ‘Be’, ‘Eesaa came into being. Regarding the other name, ‘the Spirit of Allaah’, the meaning is clear - that he is one of the spirits that Allaah The Almighty created. The genitive mode was used to honor ‘Eesaa and this mode is also used for example in the saying ‘the House of Allaah’, ’the she-camel of Allaah’, and so on. In the Quran, Allaah The Almighty Says to the angels about Aadam (what means): {And when I have proportioned him and breathed into him of My Spirit, then fall down to him in prostration.}[Quran 15: 29] Allaah The Almighty says here that He breathed into Aadam from His Spirit, however, this in no way implies or entails that he is the son of Allaah The Almighty.

And Allaah Knows best.