Abu Hurairah (May Allah be pleased with him) reported:
A black woman (or probably a young man) used to clean the mosque. Messenger of Allah ﷺ missed her (or him) and asked about her (or him). He was told that she (or he) had died. He ﷺ said, "Why did you not inform me?" (It seemed as if) they (Companions) considered the matter insignificant. Then he ﷺ said, "Show me her (or his) grave." When it was shown to him, he offered (Janazah-funeral) prayer over it and said, "These graves cover those in them with darkness, and Allah illumines them for the inmates as a result of my supplication for them".

[Al-Bukhari and Muslim].

وعنه أن امرأة سوداء كانت تقم المسجد، أو شابا، ففقدها، رسول الله ﷺ، فسأل عنها أو عنه، فقالوا: مات. قال: " أفلا كنتم آذنتموني" فكأنهم صغروا أمرها، أو أمره، فقال: " دلوني على قبره" فدلوه فصلى عليه، ثم قال: " إن هذه القبور مملوءة ظلمة على أهلها، وإن الله تعالى ينورها لهم بصلاتي عليهم" ((متفق عليه)). (23)