Sunan an-Nasa'i, Volume 3, Book 21, Hadith 2058 (DarusSalam) ⓘ
It was narrated that: Al-Bara said about Allah will keep firm those who believe, with the word that stands firm in this world and in the Hereafter "It was revealed concerning the torment of the grave.
أَخْبَرَنَا إِسْحَاقُ بْنُ مَنْصُورٍ، قَالَ حَدَّثَنَا عَبْدُ الرَّحْمَنِ، عَنْ سُفْيَانَ، عَنْ أَبِيهِ، عَنْ خَيْثَمَةَ، عَنِ الْبَرَاءِ، قَالَ { يُثَبِّتُ اللَّهُ الَّذِينَ آمَنُوا بِالْقَوْلِ الثَّابِتِ فِي الْحَيَاةِ الدُّنْيَا وَفِي الآخِرَةِ } قَالَ نَزَلَتْ فِي عَذَابِ الْقَبْرِ .
also referenced under: Hadith 2056 (Reference) & Book 21, Hadith 240 (In-Book)