According to historian Welch,
The really powerful factor in Muhammad's life and the essential clue to his extraordinary success was his unshakable belief from beginning to end that he had been called by God. A conviction such as this, which, once firmly established, does not admit of the slightest doubt, exercises an incalculable influence on others. The certainty with which he came forward as the executor of God's will gave his words and ordinances an authority that proved finally compelling.
[8]
Credit is all given to divine revelation of he prophet. And the plagiarized ideas were changed to what they call the correct version.
Which supports my claim of belief in authorship not your view.
The biblical ideas were taken by islam and put into their own text, as indicated by the two examples I have provided
Which were references to previous scripture as per belief in authorship
Carlyle's view has been increasingly influential ever since and contemporary historians tend to say that as far as can be ascertained
Muhammad did believe that he was hearing the word of God