It would be madness at least, or deep heresy at worst.
Or, it would be some sections of Abbasid Baghdad or parts of Moorish Spain.
Regarding the Prophet and cross-religious boundaries... I guess nobody here has done much interfaith work IRL? Because if you have, you know that if two faiths are both committed to the idea that their teachings relate to the "Real, Ultimate Nature of Things" then they will take a powerful interest in each others' teachings, and tend to regard each others' highest figures as intellectual authorities (though not necessarily right for that). Consider that many Christian thinkers cited Avicenna, and much Ottoman law cited cases from Orthodox ecumenical rules as authoritative.
The idea that, in a medieval setting, members of one faith would just say that the leader of another faith is bogus without anything to say or without a perspective on the Real, Ultimate Nature of Things is not very tenable,
unless there is a strong political motivation to make such a claim. But from a purely intellectual position, Medieval Christian thinkers may have thought their Muslim counterparts were implicitly worshipping demons, but they at least thought they were worshipping
very smart demons with lots of interesting knowledge, a la Faustus.
