Isn't Sinbad pre-Prophet in time?
There are no known pre-Islamic sources for the Sinbad legend. He's associated with the era of the Abbasid caliphate, and I found an article
asserting that the tales were based on the real experiences of a Persian mariner from the late 8th century, over 150 years into the Islamic era.
Besides, whatever their origins, the tales have been an important part of Islamic culture for over a millennium, not unlike King Arthur is to England. Indeed, the historical basis for Arthur may well have been a Cornish chieftain fighting against
the Anglo-Saxon conquest of his land, and yet he somehow ended up being appropriated as the archetypal national hero of his enemies' descendants. So the origins of beloved cultural heroes and myths isn't always relevant to the emotions associated with them.