Sunan Abu Dawud
667
Sahih+2

Narrated Anas ibn Malik: The Prophet (ﷺ) said: Stand close together in your rows, bring them near one another, and stand neck to neck, for by Him in Whose hand my soul is, I see the devil coming in through openings in the row just like a small black sheep

SahihMuhammad Muhyi Al-Din Abdul Hamid
SahihShuaib Al Arnaut