Allama Hasan Musa Naubahti in his book “Firag ush shia” wrote:
“Some people of knowledge  from companions of Ali said that: “Abdulla ibn Saba was yahudi who accepted islam. He was supporter of Ali . While a Jew, he propounded the exaggerative notion that Yusha ibn Nun was divinely appointed to succeed Prophet Musa, after accepting islam, he adopted a similar stance with regard to `Ali in relation to the Holy Prophet (after his death). He (ibn Saba) was the first man who told that believe in imamat of Ali is obligatory, and he openly vitriolated his enemies (i.e. the first three Caliphs) and branded them as infidels. That is why those who opposses to shia say:”The origin of Rafd is thus based on Judaism””