Sahih Al Bukhari Hadith Number 719

Narrated Anas bin Malik: Once the Iqama was pronounced and Allah’s Messenger (peace be upon him) faced us and said, “Straighten your rows and stand closer together, for I see you from behind my back.’

10  Call to Prayers (Adhaan)
Hadith number 719
Volume no 1
Chapter: 72 (Facing of the Imam towards his followers while straightening the rows.)