Bulugh al-Maram, Book 16, Hadith 1547 (English)

A’ishah (RAA) narrated that the Messenger of Allah said: “Avoid reviling the dead, they have already seen the result of (the deeds) that they forwarded before them.” Related by Al-Bukhari.

وَعَنْ عَائِشَةَ ‏-رَضِيَ اَللَّهُ عَنْهَا‏- قَالَتْ: قَالَ رَسُولُ اَللَّهِ ‏- صلى الله عليه وسلم ‏-{ لَا تَسُبُّوا اَلْأَمْوَاتَ ; فَإِنَّهُمْ قَدْ أَفْضَوْا إِلَى مَا قَدَّمُوا } أَخْرَجَهُ اَلْبُخَارِيُّ.‏ (1966)‏.‏ ‏1 ‏- صحيح.‏ رواه البخاري (1393)‏.‏

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also referenced under: Book 16, Hadith 1504 (In-Book)