Lit. foundation. Early Ismaili authors, like Ibn Hawshab (d. 914) and his son Jafar (d. 2nd half of 10th century) divided history into seven eras, each inaugurated by a speaking prophet (natiq), who is succeeded by a legatee, also called asas, the founder, a teaching based on the knowledge of the spiritual meaning of the message delivered by the Prophet. In this system of thought, Ali b. Abi Talib (d. 661) is the foundation of the imamat in the cycle of Muhammad. The writing of later Ismaili authors such as al–Nasafi (d. 943), Abu Hatim al–Razi (d. 934), Abu Yaqub al–Sijistani (d. after 971), present variants of this system. al–Sijistani, for instance, defines both the prophet and his legatee as asas.