Some of the elderly or injured congregants pray seated on chairs. Sometimes they do this by putting the back of the chair on the line and keep themselves in line with respect to their shoulders and not their feet. Other times they line up with the back of the chair extending into the line behind them, keeping their feet in line and not their shoulders. Which is preferred?
Clearly it is not possible for them to keep their feet and their shoulders in line. In such a case the priority is to keep their shoulders in line and therefore not extend the chair back into the line behind them. The Prophet (pbuh) would straighten the lines with particular emphasis on the shoulders. It also has the added benefit of not disturbing the people who are praying in the row behind them.
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