Sahih Muslim 2579
Sahih Muslim · Book 45: The Book of Virtue, Enjoining Good Manners, and Joining of the Ties of Kinship · The Prohibition Of Oppression
Ibu 'Umar reported Allah's Messenger (ﷺ) as saying:
حَدَّثَنِي مُحَمَّدُ بْنُ حَاتِمٍ ، حَدَّثَنَا شَبَابَةُ ، حَدَّثَنَا عَبْدُ الْعَزِيزِ الْمَاجِشُونُ ، عَنْ عَبْدِ اللَّهِ، بْنِ دِينَارٍ عَنِ ابْنِ عُمَرَ ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " إِنَّ الظُّلْمَ ظُلُمَاتٌ يَوْمَ الْقِيَامَةِ " .
Oppression is the darkness on the Day of Resurrection.