Christianity had a 600-or-so years headstart on it and Judaism had been practiced for a couple thousand years, neither of which the Arabs seemed to have embraced.
Was there a common religion?
The arabs had a polytheistic religion where different gods were worshipped in different places. They were some similarities to Islam, such as circling the stone in Mecca seven times and throwing rocks at the demons afterwards. Also belief in jinns is a holdover.
Christianity and probably to a lesser extent Judaism had also been practiced in some places in the Arabian penninsula. The ruins of one pre-Islamic Christian church still exist in Saudi Arabia. I don’t know if it was ever excavated (or otherwise formally documented and studied), but the Saudi authorities have it fenced off, probably to prevent vandalism and assist in its preservation.
Certianly the prophet was aware of the teachings of both in some detail, as Jesus, Mary, and many Old Testament figures are also mentioned in the Koran.
As I recall (and please correct me if I am wrong), the Koran in at least some cases suggests that the readers are already familiar with some of these “Biblical” persons. So it is likely that what we might call “Bible Stories” were familiar to many people there, even if they were not total believers.
http://www.wsu.edu/~dee/ISLAM/PRE.HTM
Also a lot of zoroastrianism flying around - though mainly in Persia, whose people weren’t actually Arabs.