Many people would say that a person cannot speak after death. However, Allah may give this power to a particular person. This has been accepted by Scholars of Ahlu Sunnah as well, like We find Ismaeel al Bukhari writing in his Tareekh-ul-Kabeer, 3/383

1281- زَيد بْنُ خَارِجَةَ بْنِ أَبي زُهَير، الخَزرَجيّ، الأَنصاريّ.
شَهِدَ بَدْرًا، تُوُفِّي زَمَانَ عُثمان، هُوَ الَّذِي تَكَلَّمَ بَعْدَ الْمَوْتِ.

Zaid bin Kharija bin Abi Zuhair al Khizraji al Ansari

He saw battle of Badr, died in era of Uthman, He was the one who spoke after death.