It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) said: "Keep your rows straight, for your rows are like the rows of the angels. Join your shoulders together, fill the gaps in between, be gentle in the hands of your brothers, and do not leave any space for Satan. Whoever joins the row, Allah joins him, and whoever breaks the row, Allah breaks him."