In Thomas Carlyle’s article, Islam is referenced to by the term “Mahometanism”, and Muslim are referenced to by the term “Mahometans”. This hints that Carlyle believed that Muhammad invented Islam, and that Islam may not be a true religion revealed to Prophet Muhammad.

Carlyle described the Quran as: “A wearisome confused jumble, crude, incondite; endless iterations, long-windedness, entanglement; most crude, incondite;--insupportable stupidity, in short! Nothing but a sense of duty could carry any European through the Koran”. This is again understandable considering the fact that Carlyle did not speak Arabic, and it was difficult for him to understand the miraculous nature of the Quran.

Draper also used the term “Mohammedanism” to reference Islam.

Draper suggested in several places in his article that the sources of Prophet Muhammad beliefs were from the Jews and Nestorians during Muhammad’s trips to Syria, and from the Jews in Medina. This is of course a gross misconception [see  The Origin of the Quran].

Referring to the Koran, Michael Hart wrote the following: “…he (Muhammad) is the author of the Moslem holy scriptures, the Koran, a collection of Muhammad’s statements that he believed had been divinely inspired.”

Gibbon did not try to hide his admiration to prophet Muhammad, but stopped short of admitting his Prophethood

Gibbon's book contains many errors in interpreting the teachings of Islam.  For example, it is not true that Muslims abstain from bathing during the month of Ramadan.  Also the alms ( zakah) on the wealth of the individual is only 2.5% and not 10% .