Is it permissible for the mosque administration to prevent those praying on chairs from praying in the first row or to compel them to pray at the end of the row even if it is not full, and do they thereby attain the reward of the first row?

One who is unable to stand during prayer may pray sitting, and he may sit on a chair. It is recommended for those praying on chairs to join the front rows, and it is not permissible to pray alone behind a row. The habit of placing chairs at the back of the mosque is a bad habit that goes against the Sunnah (definition), for the Prophet, peace and blessings be upon him, said: “If the people knew what was in the call (to prayer) and the first row, and they could not find (a way to get to it) except by casting lots, they would cast lots for it.”

The chair should be placed at the end of the row, or in its middle while filling the gaps, or moved slightly forward so that the back of the chair aligns with the row of worshipers. This is to complete the rows and fill any gaps, in compliance with the words of the Prophet, peace and blessings be upon him: "Straighten your rows, for you are aligning as the angels align. Align your shoulders, fill the gaps, and do not leave spaces for Satan. Whoever joins a row, Allah joins him, and whoever cuts off a row, Allah cuts him off." Cooperation is required among worshipers, and they should be "gentle in the hands of their brothers."