Published for The Jewish Virtual Library, a project of American-Israeli Cooperative Enterprise (AICE), the article Modern Jewish History: Great Rabbis of the Muslim Empire by Dr. Ezra Chwat is a proof of the existence of the Ismaili faith
“In 657, when Ali ibn Abu Talib — the fourth Caliph to rule after the death of Mohammed — extended the Muslim conquest into Iraq, he was greeted wholeheartedly by the Jews there, then the most important of the world’s Jewish communities. Ali saw the Jews of Iraq as a natural ally and granted them autonomy. This was the dawn of a new era of Jewish cultural creativity, one that lasted almost 600 years and was central in the development of Judaism.”
“The Lasting Contribution of the Jews of the Muslim Empire
For over 500 years, the Jews of the Muslim Empire enjoyed stability, prosperity and religious autonomy. As opposed to the oppressive atmosphere in Northern Europe, the Jews lived, for the most part, in a tolerant civilization, one that valued excellence in the arts, the sciences and trade. In these fields the Jews were welcome participants. Thus Judaism developed as part of society, not as a secluded ghetto-culture as was the case in Christian Europe. The cultural cross-pollination benefitted both sides. Because of the dialogue with Islam, the Jews became more aware of their philosophic and linguistic heritage. The new methods that developed in the vast Muslim Empire for the communication of knowledge and the codification of law were employed by the Rabbis in order to keep in contact with the ever-expanding Jewish Diaspora. Thus, they could preserve and sustain Talmudic Law, while creating new vistas of Jewish literature and thought which were instrumental in forming the structure of Judaism as it is today.”
https://www.jewishvirtuallibrary.org/great-rabbis-of-the-muslim-empire