Silsilah as-Sahihah 576 — Importance of straightening rows

Sayyiduna Abu Shajrah (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: "Straighten your rows, for you must form rows like the rows of the angels. Keep your shoulders in line, fill the gaps in the rows, and do not leave any space for Satan. Whoever joins the row, Allah will join him (with His mercy)."