Denial of the Trinity functioned as Muhammad’s defining characteristic for medieval Christian writers

Evidence

Christology was the most important of all problems for the mediaeval writer whose outlook was clerical. The Qur’anic representation of Christ had the power to fascinate; the Islamic denial of the Trinity seemed to be the basic point of difference between the religions. Guibert thought that it was the first thing popularly attributed to Muhammad; and much later Fitzralph was to characterise ‘this pseudoprophet … whose attempt was always and above all things to persuade (men) that there is no Trinity of Persons in God, and that Christ was not God’. This was almost the definition of Muhammad’s teaching: ‘Muhammad who said to his people, There is no Trinity in God, nor is Christ God.’ … It was his primary service to the Devil: ‘Nothing is so opposed to the enemy of the human race as faith in the Incarnate God.’ — Norman Daniel, Islam and the West, 970

Categorization

• XREF: The construction of the Muslim as denier-of-the-core-doctrine parallels the vault thread on how Islam is constituted as the West’s defining outside; definition by negation of the central Christian truth.