Which is regarded as the first row when some people pray next to the imam?
The first row is that which is behind the imam. So the row that is directly behind the imam is the first row, and those who form a row to his right and his left will not have the reward of the first row, because this standing -- meaning members of the congregation standing on the right and on the left -- is something that is permitted but it is not mustahabb. Standing behind the imam is undoubtedly the Sunnah, but if someone is forced to stand on his right or on his left, they may do so but that is not regarded as the first row.
Question: even though this happens every day throughout the year?
Shaykh: There is no problem with that in any case. This thing is permissible, to Allaah be praise. Their standing on his right and on his left is better than their waiting until the first group has finished. End quote.
Shaykh Muhammad ibn’Uthaymeen (may Allaah have mercy on him)