I thought it was believed that the Qur'an was dictated word-for-word by Allah to Mohammed via Gabriel.
Well, that's what he said.
Have you ever tried to take dictation? I suck at it.
And if that's the way it really happened, why did Gabriel have to keep repeating himself? Did Mohammed have a short attention span, or trouble remembering what had been said to him? One would think that an Angel of God could speak clearly and concisely.