It has been revealed to me that you will be tested in your graves with a trial close to that of the Anti-Christ
Authentic hadithعن أسماء بنت أبي بكر رضي الله عنها قالت: قام رسول الله صلى الله عليه وسلم فَذَكَرَ الفتنةَ التي يُفتن بها المرء في قبره، فلما ذكر ذلك ضَجَّ المسلمون ضَجَّةً حالت بيني وبين أن أفهم كلامَ رسول الله صلى الله عليه وسلم ، فلما سَكَنَت ضَجَّتُهم قلتُ لرجل قريب مني: أيْ -بارك الله لك- ماذا قال رسول الله صلى الله عليه وسلم في آخر قوله؟ قال: «قد أُوحِيَ إليَّ أنكم تُفتَنون في القبور قريبًا من فتنة الدَّجَّال».
Asmā' bint Abu Bakr (may Allah be pleased with her) reported that once the Messenger of Allah (may Allah’s peace and blessings be upon him) stood up and mentioned the trial with which a person will be tested in his grave. When he mentioned this, the people made a loud noise in a way that prevented me from understanding what the Messenger of Allah (may Allah’s peace and blessings be upon him) was saying. When they calmed down, I said to a man who was near me: "May Allah bless you, what did the Messenger say at the end?" He said: "It has been revealed to me that you will be tested in your graves with a trial close to that of the Anti-Christ."
Explanation
Asmā' bint Abu Bakr As-Siddīq informed that the Messenger of Allah (may Allah's peace and blessings be upon him) stood up one day to admonish people and remind them of the Hereafter. During his sermon, he started talking about the grave, its reality, and its trials in which two angels (Munkar and Nakīr) shall question man about his Lord, his Prophet, and his religion. This will be a great trial because one will be tested with regard to one's faith and certain belief. Anyone passes this test, s/he will be successful; and anyone fails,s/he will be doomed. Upon hearing this, Muslims shouted loudly out of fear from the trail of the grave, and their loud noise prevented Asmā' from hearing what the Prophet (may Allah's peace and blessings be upon him) was saying. When the noise calmed down, Asmā' asked a man who was near her, saying: "May Allah bless you, what did the Prophet say at the end of his speech?" The man told her that the Prophet (may Allah's peace and blessings be upon him) said: "Allah revealed to me that the people will be tried and tested in their graves with a trial close to that of the Anti-Christ," meaning that the trial of the Anti-Christ is as difficult and severe as the trail of the grave.
Source · Narrated by Bukhari - An-Nasaa’i
From the Hadith Encyclopedia (hadeethenc.com).