The anti-Jewish riots of 1391 drove him to North Africa. After a short stay at Miliana, he finally settled in Algiers, where he was enthusiastically welcomed. Fresh vexations awaited him, however, as another refugee, jealous of Ribash's prestige, launched a violent campaign against the newcomer in the hope that he would leave Algiers. Thanks to the intervention of R. Saul Astruc ha-Kohen, the civil authorities put an end to the conflict by appointing Isaac dayyan or communal rabbi. Their action, however, antagonized a celebrated refugee from Majorca, R. Simeon b. Zemah Duran, who declared the appointment invalid, no government having the power of jurisdiction in Jewish communal affairs. Duran relented when he was convinced that Isaac harbored no thoughts of personal aggrandizement, and the latter was left free to enjoy general affection and respect in his last years. On the anniversary of his death pilgrimages were made to his tomb until recent years.
Ribash's most important work is his responsa (Constantinople, 1546). They exercised considerable influence on subsequent halakhah, and were one of the pillars upon which the Shulhan Arukh rested. They contain a vast amount of halakhic material - part derived from sources which are no longer extant - together with much valuable information about popular customs in Spain and North Africa. The collection is of very great importance for a knowledge of the history of the Jews in those countries in the 14th century. Ribash was involved as a halakhist and decisor in the great controversy connected with the French chief rabbinate; he was one of the first to discuss the status of Marranos from the halakhic point of view, which had become one of the crucial problems of Spanish and North African Judaism. He was one of those who established the minhag of Algiers regarding the pecuniary rights connected with matrimonial law. Ribash also wrote an extensive commentary on several talmudic tractates, and a commentary on the Pentateuch. Poems and kinot composed by him were published in Zafenat Pa'ne'ah (1895).