It was narrated that 'Imran bin Husain said: "The Messenger of Allah (ﷺ) said to us: 'Your brother An-Najashi has died, so get up and offer the funeral prayer for him.' So we got up and formed row to pray for him, as rows are formed to pray for the dead, and he led us in praying for him as people pray for the dead."
Source: sunnah.com
Other translations
Arabic
أَخْبَرَنَا إِسْمَاعِيلُ بْنُ مَسْعُودٍ، قَالَ حَدَّثَنَا بِشْرُ بْنُ الْمُفَضَّلِ، قَالَ حَدَّثَنَا يُونُسُ، عَنْ مُحَمَّدِ بْنِ سِيرِينَ، عَنْ أَبِي الْمُهَلَّبِ، عَنْ عِمْرَانَ بْنِ حُصَيْنٍ، قَالَ قَالَ لَنَا رَسُولُ اللَّهِ صلى الله عليه وسلم " إِنَّ أَخَاكُمُ النَّجَاشِيَّ قَدْ مَاتَ فَقُومُوا فَصَلُّوا عَلَيْهِ " . قَالَ فَقُمْنَا فَصَفَفْنَا عَلَيْهِ كَمَا يُصَفُّ عَلَى الْمَيِّتِ وَصَلَّيْنَا عَلَيْهِ كَمَا يُصَلَّى عَلَى الْمَيِّتِ .
sunnah.com