Musnad Ahmad Hadith 12517

It is narrated from Anas (may Allah be pleased with him) that there was an Abyssinian who used to clean the mosque. One day he passed away, and the people buried him during the night. When the Prophet (ﷺ) found out, he said to the companions (may Allah be pleased with them), "Let us go to his grave." So they went to his grave. The Prophet (ﷺ) said, "There is darkness upon the dwellers of these graves. By the blessing of my prayer, Allah will illuminate them." Thus, the Prophet (ﷺ) offered the funeral prayer at his grave. Upon this, an Ansari said, "O Messenger of Allah (ﷺ)! My brother had passed away, but you did not offer the funeral prayer at his grave." The Prophet (ﷺ) asked, "Where is his grave?" The Ansari pointed it out, so the Prophet (ﷺ) went with him as well.