In my opinion, those who claim that Mohammed plagiarized from other books lack integrity. Mohammed spent 13 years after his revelation calling peacefully to the religion of Allah, and the inspiration was still coming down at the time where Quraishi unbelievers used to continuously prevent him from doing so, we all know the prophet's statement when the Qurishi pagans asked Abu Taleb the uncle of Mohammed about leaving Islam:
"By Allah, if they put the sun in my right, and the moon in my left, I wouldn't stop [calling] until Allah appears it or I am done without it"
During these 13 years Mohammed experienced lost of troubles in his mission like migration, boycott, mockings, and he was harmed in Ta'if where no one embraced Islam except one.
After this period, Mohammed was discharging armies, giving the Ahkam (rullings) he was leading the battles, and giving instructions, and the revelation was still descending down.. After that, the Prophet started sending letters to the Kings of the world, as he wanted to establish the deen over all as Allah said. And then the conquests started.
There is no way, that Mohammed plagiarized from anyone, the critics need an evidence not a hypothesis, no one will believe anyone if he speculates about an argument and doesn't give reasonable evidence.
