Sahih Bukhari

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)