Is the prayer of the imam and the congregants accepted if the imam leads them in prayer while he is doubtful about the validity of his ablution?

It is permissible for the worshiper to pray behind the Imam unless he knows that his ritual purity (taharah) is invalid. If he knows that his prayer is invalid due to his knowledge of his impurity (hadath), then it is not permissible to follow him. However, mere doubt does not prevent following him or invalidate the prayer behind him. If a person doubts the invalidation of his ablution (wudu'), the default is that his purity remains, and he is not required to perform ablution according to the majority of scholars.