Jesus was a prophet of Islam, so was Adam, Lot, Abraham, Jonah, Jospeh....all the way to Muhammad (PBU them all)

If there is one God, then all the messengers must have come with a message from Him. Logically therfore, God does not give 'mixed messages', hence the message must have been the same throughout but corrupted by men and time. Islam is not something that started 1400 years ago. it started with God, who has no begining and no end.