Language:
كتاب الأذان
10  
Call to Prayers (Adhaan)
(27)
Chapter: If the Imam is confronted with a problem after the Iqama
(27)
باب الإِمَامِ تَعْرِضُ لَهُ الْحَاجَةُ بَعْدَ الإِقَامَةِ
Sahih al-Bukhari 642

Narrated Anas:

Once the Iqama was pronounced and the Prophet (ﷺ) was talking to a man (in a low voice) in a corner of the mosque and he did not lead the prayer till (some of) the people had slept (dozed in a sitting posture) .

حَدَّثَنَا أَبُو مَعْمَرٍ عَبْدُ اللَّهِ بْنُ عَمْرٍو، قَالَ حَدَّثَنَا عَبْدُ الْوَارِثِ، قَالَ حَدَّثَنَا عَبْدُ الْعَزِيزِ بْنُ صُهَيْبٍ، عَنْ أَنَسٍ، قَالَ أُقِيمَتِ الصَّلاَةُ وَالنَّبِيُّ صلى الله عليه وسلم يُنَاجِي رَجُلاً فِي جَانِبِ الْمَسْجِدِ، فَمَا قَامَ إِلَى الصَّلاَةِ حَتَّى نَامَ الْقَوْمُ‏.‏
Reference : Sahih al-Bukhari 642
In-book reference : Book 10, Hadith 39
USC-MSA web (English) reference : Vol. 1, Book 11, Hadith 615
  (deprecated numbering scheme)