Sahih Muslim , Book 3, Hadith 154 (In-Book)

Anas reported: (The people) stood up for prayer and the Messenger of Allah was whispering to a man, and in the narration of 'Abd al-Warith (the words are): The Apostle of Allah was having a private conversation with a man, and did not start the prayer till the people dozed off.

حَدَّثَنِي زُهَيْرُ بْنُ حَرْبٍ، حَدَّثَنَا إِسْمَاعِيلُ ابْنُ عُلَيَّةَ، ح وَحَدَّثَنَا شَيْبَانُ بْنُ فَرُّوخَ، حَدَّثَنَا عَبْدُ الْوَارِثِ، كِلاَهُمَا عَنْ عَبْدِ الْعَزِيزِ، عَنْ أَنَسٍ، قَالَ أُقِيمَتِ الصَّلاَةُ وَرَسُولُ اللَّهِ صلى الله عليه وسلم نَجِيٌّ لِرَجُلٍ - وَفِي حَدِيثِ عَبْدِ الْوَارِثِ وَنَبِيُّ اللَّهِ صلى الله عليه وسلم يُنَاجِي الرَّجُلَ - فَمَا قَامَ إِلَى الصَّلاَةِ حَتَّى نَامَ الْقَوْمُ ‏.‏

sunnah.com