Those who believe and those who are Jews and the Sabaens and the Christians, whoever believes in Allah and the period hereafter and does righteous work, then certainly, there will neither be any fear on them nor will they grieve.
Whatever be the earlier creed, one who believes in Allah (SWT) and life after death and does righteous work i.e. acts in accordance with the instructions contained in the Quran, then he is successful.