A man asked, "Messenger of Allah, why is it that the believers are tested in their graves except for the martyr?"He replied, "The flashing of swords above his head is trial enough for him."
أن رجلا قال: يا رسول الله! ما بال المؤمنين يفتتنون في قبورهم إلا الشهيد؟ قال: كفى ببارقة السيوف على رأسه فتنة.
Nasai (2053) narrated it from Ibrahim bin Hasan, who said, Hajjaj narrated to us, from Layth bin Saad, from Muawiya bin Salih, that Safwan bin Amr told him, from Rashid bin Saad, from a man among the companions of the Prophet ﷺ, and he mentioned it.Its narrators are trustworthy, except that Rashid bin Saad is trustworthy but practiced tadlis by omission (irsal). He heard from a group of the companions, but narrated from Saad bin Abu Waqqas without direct hearing. There is disagreement over whether he heard from Thawban, Imam Ahmad denied it, while Bukhari affirmed it in Adab al-Mufrad.What I hope is that he heard this hadith from one of the companions and did not narrate it by irsal.