[Cronos]

Protestantism by definition is all the movements that originally split from the Western Church post the 14th century.

It does not include any movements prior to that and does not include any splits from the Eastern Orthodox or Assyrians or the Syriacs or the Copts

Islam does not fit into this definition.

Islam is a syncretic religion taking aspects of pre-islamic Arabic religions (such as djinn for example), merging it with Nestorian Christianity, Syriac, Gnostic forms of Christianity and with Judaism and Zoroastrianism -- this was not a split or a protest against Christianity -- Christianity was not a major religion in Makkah or Yathrib (what is now called Medina)

If anything, the major non-pagan religion there was Judaism

Mohammad saw a chance to unite the Arabic tribes initially using Judaism as a monotheistic uniting factor (but replacing Isaac with Ishmael as the sacrifice) and then he added Gnostic pieces (which is why Jesus in the Koran says things you don't find in the Bible but which you find in the Gnostic "Gospel of Thomas" and Jesus laughs when he is on the cross -- a Gnostic concept of Jesus not as a real man of blood and flesh -- Lady Heron, if you mean Gnostics instead of Marcionites I would agree -- because Marcion rejected the OT, while the Moslems don't.

[Kolokotronis]

“Islam is a syncretic religion taking aspects of pre-islamic Arabic religions (such as djinn for example), merging it with Nestorian Christianity, Syriac, Gnostic forms of Christianity and with Judaism and Zoroastrianism — this was not a split or a protest against Christianity — Christianity was not a major religion in Makkah or Yathrib (what is now called Medina)”

Precisely.