How can God have a son?
Not the way the Quran imagines. Son of God has never meant God took a wife. It means the eternal Word who is with God and is God, who became flesh.
The Quran asks how God could have a child without a consort. Christians agree that would be blasphemous, and no Christian has ever taught it. The Son is eternally begotten, not made: as a word comes from a mind without being a second mind, the Word was with God and was God.
101The Originator of the heavens and the earth! How can He have a child, when there is for Him no consort, when He created all things and is Aware of all things?
Quran 6:101 (Pickthall) · context
1In the beginning was the Word, and the Word was with God, and the Word was God. 2The same was in the beginning with God. 3All things were made through him. Without him, nothing was made that has been made.
John 1:1-3 (WEB) · context
14The Word became flesh and lived among us. We saw his glory, such glory as of the only born Son of the Father, full of grace and truth.
John 1:14 (WEB) · context
3His Son is the radiance of his glory, the very image of his substance, and upholding all things by the word of his power, who, when he had by himself purified us of our sins, sat down on the right hand of the Majesty on high,
Hebrews 1:3 (WEB) · context