Sayyiduna Abdullah bin Amr (may Allah be pleased with him) narrates this as a marfu' hadith: The Prophet (peace and blessings be upon him) said: "Reviling the deceased, and on one occasion the narrator said: the dead, is like one who is looking over the brink of destruction."
Al-Tabarani recorded it, and its narrators are the narrators of the Sahih.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الأدب / 13033