Sunan An-Nasa'i - سنن النسائي
10. The Book of Leading the Prayer (Al-Imamah) - كتاب الإمامة
13) Chapter: If something comes upon the Imam after the iqamah has been said
It was narrated that Anas said:
"The Iqamah for prayer was said, and the Messenger of Allah (ﷺ) was conversing privately with a man, and did not commence the prayer until the people slept."
13) باب الإِمَامِ تَعْرِضُ لَهُ الْحَاجَةُ بَعْدَ الإِقَامَةِ
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 .