Does a worshipper receive the reward for congregational prayer in a small mosque where the call to prayer is made, and the number of worshippers is small?

Congregational prayer in small mosques has a multiplied reward, just like in other mosques. The place designated for prayer, where the call to prayer (adhan) is made and a congregation (jama’ah) is held, earns the reward of congregational prayer regardless of whether it is called a musalla (prayer room) or a zawiya (small prayer house), because a congregation is formed by two or more people. The reward for congregational prayer is attained by whoever prays in a place prepared for prayer. The mosque with a larger congregation is better, however, the mosque of one's neighborhood, even if its congregation is small, is better than the grand mosque, even if its congregation is large. The difference between a mosque and a musalla is that a mosque is an endowment (waqf) for prayer, whereas a musalla retains its owner's private ownership. The reward for congregational prayer is multiplied whether it is performed in a musalla or a mosque.