What the Jewish Encyclopedia Has to Say About Ibn Saba'

[Abu Jasim Al-Salafi]

This is what the Jewish Encyclopedia says about Abdullah Ibn Saba':

"A Jew of Yemen, Arabia, of the seventh century, who settled in Medina and embraced Islam. Having adversely criticized Calif Othman's administration, he was banished from the town. Thence he went to Egypt, where he founded an antiothmanian sect, to promote the interests of Ali. On account of his learning he obtained great influence there, and formulated the doctrine that, just as every prophet had an assistant who afterward succeeded him, Mohammed's vizier was Ali, who had therefore been kept out of the califate by deceit. Othman had no legal claim whatever to the califate; and the general dissatisfaction with his government greatly contributed to the spread of Abdallah's teachings. Tradition relates that when Ali had assumed power, Abdallah ascribed divine honors to him by addressing him with the words, "Thou art Thou!" Thereupon Ali banished him to Madain. After Ali's assassination Abdallah is said to have taught that Ali was not dead but alive, and had never been killed; that a part of the Deity was hidden in him; and that after a certain time he would return to fill the earth with justice. Till then the divine character of Ali was to remain hidden in the imams, who temporarily filled his place. It is easy to see that the whole idea rests on that of the Messiah in combination with the legend of Elijah the prophet. The attribution of divine honors to Ali was probably but a later development, and was fostered by the circumstance that in the Koran Allah is often styled "Al-Ali" (The Most High)."

Bibliography:
Shatrastani al-Milal, pp. 132 et seq. (in Haarbrücken's translation, i. 200-201);
Weil, Gesch. der Chalifen, i. 173-174, 209, 259.

Source: http://jewishencyclopedia.com/articles/189-abdallah-ibn-saba