Sunan an-Nasa'i, Hadith 2042 ⓘ
It was narrated that Abu Hurairah: Said that the Messenger of Allah announced the death of An-Najashi, the ruler of Ethiopia, to them on the day that he died, and said "Pray for forgiveness for your brother."
أَخْبَرَنَا أَبُو دَاوُدَ، قَالَ حَدَّثَنَا يَعْقُوبُ، قَالَ حَدَّثَنَا أَبِي، عَنْ صَالِحٍ، عَنِ ابْنِ شِهَابٍ، قَالَ حَدَّثَنِي أَبُو سَلَمَةَ، وَابْنُ الْمُسَيَّبِ، أَنَّ أَبَا هُرَيْرَةَ، أَخْبَرَهُمَا : أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم نَعَى لَهُمُ النَّجَاشِيَّ صَاحِبَ الْحَبَشَةِ فِي الْيَوْمِ الَّذِي مَاتَ فِيهِ فَقَالَ : " اسْتَغْفِرُوا لأَخِيكُمْ " .
also referenced under: Book 21, Hadith 226 (In-Book) & Volume 3, Book 21, Hadith 2044 (DarusSalam)