Abu Huraira reported Allah's Messenger (ﷺ) as saying:

By Him in Whose Hand is my life, a time would come when the murderer would not know why he has committed the murder, and the victim would not know why he has been killed.

Reference	: Sahih Muslim 2908 a
In-book reference	: Book 54, Hadith 69
USC-MSA web (English) reference	: Book 41, Hadith 6949