Riyad as-Salihin (The Meadows of the Righteous)
by Imam Nawawi
267. Chapter: On the prohibition against abusing the dead without cause and benefit in the Shari'a
That is cautioning against following his innovation, impiety and the like of that.
1564. 'A'isha reported that the Messenger of Allah , may Allah bless him and grant him peace, said, "Do not curse the dead. They have arrived at what they sent ahead." [al-Bukhari]