Hazrat Mus'ab bin Sa'd (may Allah have mercy on him) narrates that Hazrat Ali (may Allah be pleased with him) bin Abi Talib said a few words and spoke absolutely correctly: That is, it is obligatory upon the Imam to judge according to the Qur'an revealed by Allah, and to fulfill the trust. And if he does so, then it is obligatory upon the Muslims to listen to him and obey him. And when they are called, they should respond to the call.