Synagogue of Satan
In the letters to the early Christian churches of Smyrna and Philadelphia in Revelation 2:9 and 3:9, reference is made to a synagogue of Satan (Greek: συναγωγή τοῦ Σατανᾶ, synagoge tou satana), in each case referring to a group persecuting "who say they are Jews and are not".
Revelation 2:9 King James Version (KJV)
9 I know thy works, and tribulation, and poverty, (but thou art rich) and I know the blasphemy of them which say they are Jews, and are not, but are the synagogue of Satan.
Revelation 3:9 King James Version (KJV)
9 Behold, I will make them of the synagogue of Satan, which say they are Jews, and are not, but do lie; behold, I will make them to come and worship before thy feet, and to know that I have loved thee.