An-Nu’man ibn Bashir said: “The Messenger of Allah (peace be upon him) paid attention to the people and said three times; straighten your rows (in prayer); by Allah, you must straighten your rows, or Allah will certainly put your faces in contrary directions. I then saw that every person stood in prayer keeping his shoulder close to that of the other, and his knee close to that of the other, and his ankle close to that of the other.” (Abu Dawud)
Here, Sheikh Muhammad Salah talks in brief about the techniques of how to line up in the rows after the imam during prayer.
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