Sunan an-Nasa'i, Volume 1, Book 10, Hadith 792 (DarusSalam)

It was narrated that Anas said: "The Iqamah for prayer was said, and the Messenger of Allah was conversing privately with a man, and did not commence the prayer until the people slept."

أَخْبَرَنَا زِيَادُ بْنُ أَيُّوبَ، قَالَ حَدَّثَنَا إِسْمَاعِيلُ، قَالَ حَدَّثَنَا عَبْدُ الْعَزِيزِ، عَنْ أَنَسٍ، قَالَ أُقِيمَتِ الصَّلاَةُ وَرَسُولُ اللَّهِ صلى الله عليه وسلم نَجِيٌّ لِرَجُلٍ فَمَا قَامَ إِلَى الصَّلاَةِ حَتَّى نَامَ الْقَوْمُ ‏.‏

sunnah.com