Ibn Shihab (may Allah have mercy on him) says that the Messenger of Allah (peace and blessings be upon him) said: "Two religions shall not come together in the Arabian Peninsula." (b) Ibn Shihab says: Umar (may Allah be pleased with him) investigated this until he received satisfaction and certainty from the Messenger of Allah (peace and blessings be upon him) that he said: "Two religions shall not be gathered together in the Arabian Peninsula." So he expelled the Jews of Khaybar. Imam Malik (may Allah have mercy on him) says that Umar (may Allah be pleased with him) expelled the Jews of Najran and Fadak.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجزية / 18751