Is it permissible to pray behind an Imam who does not master the rules of prayer?

If the Imam violates a condition, a pillar, or an obligatory duty of the prayer, then the prayer behind him is invalid, and he must be taught the rulings of the prayer. However, if he violates some of the etiquettes and Sunan (recommended practices) of the prayer, this does not invalidate his prayer, and it is not permissible to abandon praying behind him for that reason, unless another Imam is found who is more observant of the Sunan and etiquettes, in which case one should pray behind him.