It was only when Al-Muktadir was killed in a rebellion (October, 932), and Kahir, who was so poor that he was obliged to borrow clothes for the ceremony of installation, became Caliph, that David's party, which could pour more money into the empty treasury, gained the victory. In order to bring about the downfall of his opponent, the Exilarch squandered the money that had been extorted from the various communities. Saadiah was soon forbidden by the Caliph to continue in office, perhaps also to stay in Sora (commencement of 933). The rival Exilarch Hassan was banished to Khorasan, where he died. Saadiah now lived in retirement in Bagdad for four years (933-937). His health had suffered severely through the constant quarrels and the annoyance he had received, and he became melancholy. But this did not interfere with his intellectual activity. It was during his retirement that his best works, bearing the stamp of freshness and originality, were written. He wrote Talmudic treatises, composed poetical pieces and prayers in prose, full of religious fervor. He also arranged a prayer book (Siddur), after the manner of Amram, collected the rules of the calendar (Ibbur), wrote a polemic against the Massoret, Aaron ben Asher, of Tiberias, and was in general particularly prolific in literary composition during this period. The greatest of his works, however, are his two philosophical writings, the one a commentary on the "Book of the Creation" (Sefer Yezirah), the other his _magnum opus_ on Faith and Creed. Both these works are in Arabic. Saadiah was the first to set up a tolerably complete system of religious philosophy. The Karaite teachers, it is true, were fond of lengthy philosophical disputations, which they frequently introduced on most unsuitable occasions, but they were never able to develop a complete and perfect religious system, and the Arabs, too, had as yet no systematic philosophy. Saadiah, by his own unaided intellectual power, built up a Jewish philosophy of religion, although he borrowed his method of treatment and his philosophical themes from the Arabic Mutazilist school. His composition on the Ten Commandments, in which he strove to bring them into relation with the Ten Categories of the Aristotelian philosophy, belongs to his earlier and less excellent efforts.