The most widespread pattern of forming secondary imperfectives in Slavic is exemplified by the following Old Church Slavonic type:
pasti, padǫ (perfective) → padati, padajǫ (imperfective)
obrězati, obrěžǫ → obrězati, obrězajǫ
sъzьdati, sъziždǫ → sъzidati, sъzidajǫ
narešti, narekǫ → naricati...