Ali 'Imran 3:100

Ya ayyuha allatheena amanooin tuteeAAoo fareeqan mina allatheena ootoo alkitabayaruddookum baAAda eemanikum kafireen

O you who have believed, if you obey a party of those who were given the Scripture, they would turn you back, after your belief, [to being] unbelievers.

O you who believe, if you obey a group from those who have been given the Book (i.e. the Christians and the Jews), they will turn you into infidels after you have embraced the faith.