It is correct that Christians & Muslims believe that Jesus will come back one day, Inshallah.
Though I've heard from my Jewish companions that they don't believe that Jesus will come back because it is not metioned in the Torah. Only the Quran and the Bible.
Christians and Muslims do not believe in the same Messiah. The Muslims believe that there was a man called Jesus, but they believe that he was only a prophet and he died just the same as any other man. The Jews believe that the Messiah has not come yet. They are looking for a conquering king, instead of Jesus the Servant, as He was the first time.
The operative word here is 'if' - and they do not!
Christ is the messiah, the Son of the living God, promised from the beginning -
islam denies the messiah, claiming God never had a Son -
'he who denies the Son, denies Him who sent Him'