مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3818
Musnad of Abdullah bin Mas'ood
It was narrated that Shaqeeq said: I was sitting with "Abdullah and Abu Moosa, when they were talking and they said: The Messenger of Allah (ﷺ) said: "Ahead of the Hour there will be some days in which knowledge will be taken away and ignorance will prevail, and there will be a lot of harj.” And harj means killing
Musnad Ahmad 3841lts isnad is saheeh, al-Bukhari (2062) and Muslim (2672)]