To who says Prophet Muhammed(pbuh)wrote Koran,Koran reply on them?

I believe the verse you are quoting is Allah telling the people that if Muhammad (peace be upon him) had fabricated the sayings in the Qur'an against Allah and His Greatness (us). It's a common way of speaking in the Arabic tongue at the time to say things like my strength and I will defeat you, or my knowledge and I will figure this out. That's whats going on in this verse. Allah (God) knows best!