﴿ مَا كَانَ لِلَّهِ أَن يَتَّخِذَ مِن وَلَدٍۢ ۖ سُبْحَٰنَهُۥٓ ۚ إِذَا قَضَىٰٓ أَمْرًۭا فَإِنَّمَا يَقُولُ لَهُۥ كُن فَيَكُونُ ﴾

“It is not conceivable that God should have taken unto Himself a son: limitless is He in His glory! When He wills a thing to be, He but says unto it "Be" -and it is!”

It is not befitting for God to take to Himself a son. Glory be to Him — in affirmation of His being transcendent above doing such a thing. When He decrees a thing that is when He will for it to happen He only says to it ‘Be!’ and it is read fa-yakūnu because of an implied pronoun huwa sc. fa-huwa yakūnu; or read fa-yakūna because of an implied an sc. an yakūna. An example of this is His creating Jesus without his having had a father.