Sayyiduna Abu Umamah (may Allah be pleased with him) said: I heard the sermon of the Prophet (peace and blessings be upon him) in the year of the Farewell Pilgrimage. He (peace and blessings be upon him) said many good and beautiful things, among which was: "Whoever of the people of the two Scriptures accepts Islam will have his reward twice; he will have the same as what we have, and he will bear the same responsibility as we bear. And whoever of the idolaters accepts Islam will have his reward; he will have the same as what we have, and he will bear the same responsibility as we bear."
Hadith Referenceالمعجم الكبير للطبراني / باب الصاد / 7755