Is prayer valid behind an imam about whom nothing is known, and who has been temporarily appointed by the mosque's organizers due to the unavailability of official mosques?

Congregational prayer is obligatory, and keenness to perform it is required. Prayer behind an Imam whose فسق (disobedience/corruption) is confirmed is valid. Thus, it is all the more valid behind someone whose فسق is unknown. Do not raise doubts about the validity of prayer behind an Imam whose state is concealed (i.e., not openly known to be disobedient), as long as nothing has become apparent from him that would invalidate his prayer or prayer behind him. It is not a condition for the worshipper to know the Imam's beliefs or to test him; rather, one prays behind someone whose state is concealed.