Imam Ahmad on Boycotting the Khawarij

Al-Khallāl records that Imām Aḥmad – may Allāh have mercy on him – said about the Khawārij:

Do not sell food or clothes to them, and do not buy from them. And he said, The Khawārij are renegades, an evil people.

Al-Khallāl, Al-Sunnah 1:155