Is it permissible to pray in a mosque where the muezzin and imam accuse people, backbite about them, and oppress them, and delay the prayer many times?

A Muslim is not permitted to backbite, oppress, or unjustly supplicate against his Muslim brother. If the Imam does so, it does not justify abstaining from congregational prayer. One can avoid the times when these things occur. If the prayer is established, one should join the congregation, or pray with another congregation outside the mosque or in another mosque.

If delaying the prayer from its time means only delaying it from its earliest time, then it is obligatory to wait for the congregational prayer. Some scholars choose in this case to perform the prayer twice: once individually at the beginning of the time, and once with the congregation at its end. However, if the delay reaches the point of the entire time expiring, then it is not permissible to wait.