The Jewish Foundation of Islam

This is an excellent book. The author, Charles Cutler Torrey, was chair of the Semitic languages department at Yale; he was a serious polyglot, he knew Hebrew and Aramaic, Latin and Greek, German and French.

The Jewish Foundation of Islam - PDF download

Mohammed had little knowledge of Christianity; he thought the Trinity was Allah, Jesus, and Mary. He had no knowledge of Daniel, or most of the prophets. His religious education was from rabbis, but was far from thorough.

Having said that, Sufism is not dependent upon Islam or the Koran. The Sufis produced some of the best religious poetry, and made important contributions to science.