Sunan an-Nasa'i, Book 21, Hadith 249 (In-Book) ⓘ
It was narrated from Aishah that: the Prophet used to seek refuge with Allah from the torment of the grave and the trial of the Dajjal, and he said: "You will be tested in your graves."
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا سُفْيَانُ، عَنْ يَحْيَى، عَنْ عَمْرَةَ، عَنْ عَائِشَةَ، أَنَّ النَّبِيَّ صلى الله عليه وسلم كَانَ يَسْتَعِيذُ مِنْ عَذَابِ الْقَبْرِ وَمِنْ فِتْنَةِ الدَّجَّالِ وَقَالَ " إِنَّكُمْ تُفْتَنُونَ فِي قُبُورِكُمْ " .
also referenced under: Hadith 2065 (Reference) & Volume 3, Book 21, Hadith 2067 (DarusSalam)