Sunan Ibn Majah, Hadith 1600 ⓘ
It was narrated from Fatimah bint Husain that her father said: The Prophet said: “Whoever was stricken with a calamity and when he remembers it he says ‘Inna lillahi, wa inna ilayhi raji’un (Truly, to Allah we belong and truly, to Him we shall return),’ even though it happened a long time ago, Allah will record for him a reward like that of the day it befell him.”
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا وَكِيعُ بْنُ الْجَرَّاحِ، عَنْ هِشَامِ بْنِ زِيَادٍ، عَنْ أُمِّهِ، عَنْ فَاطِمَةَ بِنْتِ الْحُسَيْنِ، عَنْ أَبِيهَا، قَالَ قَالَ النَّبِيُّ ـ صلى الله عليه وسلم ـ " مَنْ أُصِيبَ بِمُصِيبَةٍ فَذَكَرَ مُصِيبَتَهُ فَأَحْدَثَ اسْتِرْجَاعًا - وَإِنْ تَقَادَمَ عَهْدُهَا - كَتَبَ اللَّهُ لَهُ مِنَ الأَجْرِ مِثْلَهُ يَوْمَ أُصِيبَ " .
also referenced under: Book 6, Hadith 1668 (In-Book) & Volume 2, Book 6, Hadith 1600 (DarusSalam)