From Sahih Bukhari (Hadith 1327):
Narrated Abu Huraira:Allah's Messenger (ﷺ) informed about the news of the death of An-Najash (King of Ethiopia) on the day he expired. He said, "Ask Allah's forgiveness for your brother. " Narrated Abu Huraira: The Prophet (ﷺ) made them align in rows at the Musalla and said four Takbir
Reference: Bukhari 1327