Bukhari 85

Narrated Abu Huraira:The Prophet (ﷺ) said, "(Religious) knowledge will be taken away (by the death of religious scholars) ignorance (in religion) and afflictions will appear; and Harj will increase." It was asked, "What is Harj, O Allah's Messenger (ﷺ)?" He replied by beckoning with his hand indicating "killing." (Fath-al-Bari Page 192, Vol)