Q: At our local masjid, there is no regular imam. Often, a different person is appointed close to the time of prayer to lead the prayers. Usually the person will not have a long enough beard and/or will be wearing western clothing. Is it permissible to pray behind them? Am I required to insist that a person with proper external qualities lead the prayer, even if I am the only one?
A: 1) Salaah behind such people is valid. There is no need to repeat the salaah.
2) If you are a trustee of the musjid then you must insist that such people do not lead salaah and that a proper Imam is appointed. If you are not a trustee then you cannot insist or demand. Yes you can suggest to the trustees or make a request that they appoint a proper Imam. If there is another Musjid nearby where you can offer salaah behind an Imam who meets the Shar'ee requirements, then rather attend that Musjid. If there is no such musjid nearby then continue reading salaah in this musjid regardless of who leads the salaah. Your salaah will be valid and you will attain the reward of jamaat.
Mufti Siraj Desai