How is free will in humans logically justified?

I had an argument with a friend who wanted me to logically or with a reference tell him, that if Allah has decided everything for us. E.g, if I pick a glass and put it at another place, if that is decided (as Qur'an says, that our life has been written), then where is the free will because our fate has been decided, i.e., if Allah has given us free will, then how can we say that everything we do in life is already written? In the same context, why do we have angels on our shoulders writing down every thing wrong and good, if Allah knows our intention and already decided our fate even before we were born
Is there any reference or Ayah or Hadith regarding it?