Sayyiduna Ibn Abbas (may Allah be pleased with them both) narrates: When Sayyiduna Abdullah bin Salam, Tha'labah bin Sa'yah, Asad bin Ubayd and those of the Jews who accepted Islam believed, affirmed the truth and became devoted to Islam, the disbelieving rabbis of the Jews said: None have believed in Muhammad and followed him except the worst of us; had they been among the best of us, they would not have abandoned the religion of their forefathers. So Allah, the Mighty and Majestic, revealed in response to this statement of theirs: "They are not all alike: among the People of the Book is an upright community; they recite the verses of Allah during the hours of the night and they prostrate. They believe in Allah and the Last Day, they enjoin what is right and forbid what is wrong, and they hasten to good deeds, and those are among the righteous." [Surah Al Imran: 113-114]
Hadith Referenceالمعجم الكبير للطبراني / باب الثاء / 1375