It is not obligatory upon every Muslim to be an imam, but those who have taken the position of imam have certain duties to perform. If a person is too old to perform those duties properly or has become disabled due to some sickness or accident, then he can be retired from his position. As for obtaining a salary from either the mosque board or from the government, there is nothing wrong with that and those imams should be supported by the states where they live in order to enable them to meet their requirements.
Dr. Muzammil H. Siddiqi, current president of the Fiqh Council of North America, states the following: There is no “retired Muslim.” A person has to continue doing his or her obligations as a Muslim until the end of life. But imam is a position to which a person is appointed by the community. It is not obligatory upon every Muslim to be the imam, but those who have taken the position of imam have certain duties to perform. The position of imam could be full-time or part-time. The imam has to perform some duties for the community. If a person is too old to perform those duties properly, or has become disabled due to some sickness or accident, then he can be retired from his position. As long as a person is able to fulfill his responsibilities as imam, there is no need to retire him. The communities that have full-time imams should provide retirement benefits to them so that they are not disgraced by poverty and begging after they leave their position of respect and honor.
A person can perform the duties of imam voluntarily or he can be paid for them. All jurists (fuqahaa’) agree that it is permissible to pay a person for teaching the Qur’an, for making the Adhan or for leading the Prayers. This is because they say that a person is asked to do what he is not obligated to do. In the language of the Shari`ah this is called “ilzamma la yalzam” (making compulsory something on a person which is not compulsory on that person). Since the community is asking a person to be available at certain time and to lead the Prayer in a certain place, or teach or do similar things, then the person is entitled to receive some compensation, unless he is able to do these things voluntarily. It is better for those who can afford it to perform these duties voluntarily, but receiving payment is not forbidden.