What is the prescribed action for an arriving follower (Ma'mum) finding a gap in the prayer row?
Chapter on Imamate and Congregational Prayer
Al-Mughni
Book of Prayer
Primary text
If a follower enters the prayer and finds a gap in the row, he must enter that gap. If no gap is found, he stands to the right of the Imam. The preferred action is not to pull a person to stand with him in a new row. This view is supported by the statement regarding the Prophet, peace be upon him: "Be gentle in the hands of your brothers," which is interpreted to mean this action.
Supporting text
Ata and Al-Nakha'i permitted pulling a person to form a row with the newcomer. Malik and Al-Awza'i disliked this action, and Ahmad and Ishaq found it reprehensible. Ibn Aqil permitted it according to his companions but preferred not to do it due to the unauthorized disposition of another's action.