Is it permissible to pray behind an Imam in a prayer hall that was formerly a commercial establishment, where the Imam stands in a corner and some worshippers stand in front of him, with a barrier separating them?

The scholars differed on the validity of a congregant's prayer in front of the Imam, with three opinions:

1. First opinion: It is valid, though disliked if without an excuse, and valid without being disliked if there is an excuse, such as a constricted mosque. This is the view of the Malikis.

2. Second opinion: It is not valid absolutely. This is the view of Abu Hanifa and Shafi'i, and the well-known position of Ahmad within their schools.

3. Third opinion: It is valid only with an excuse. This is a position within Imam Ahmad's school chosen and preferred by Shaykh al-Islam Ibn Taymiyyah.

Accordingly, the prayer of a congregant in front of the Imam is not valid unless there is an excuse. If there is no excuse, their prayer is not valid. However, if there is an excuse (such as a constricted mosque), the prayer of everyone is valid.