Abu Dawud Book 2, Hadith Number 666.
Chapter : Not known.
Narated By Abdullah ibn Umar : The Prophet (PBUH) said: Set the rows in order, stand shoulder to shoulder, close the gaps, be pliant in the hands of your brethren, and do not leave openings for the devil. If anyone joins up a row, Allah will join him up, but if anyone breaks a row, Allah will cut him off.