The late great scholar, 'Abdul-Azeez Bin Baz was very vocal against the extremist takfiri
groups that emerged and became prominent in the 80s and 90s with killing innocents and committing actions of terrorism
. In a cassette recording made as far back as 1987, that's right 1987
, Shaikh Ibn Baz gave the following answer in response to the question:
Concerning Jamaa'at ul-Jihaad and co-operation with them?
Answer: They are not to be co-operated with, nor are they to be given salaams to. Rather, they are to be cut off from, and the people are to be warned against their evil. Since they are a fitnah (tribulation) and are harmful to the Muslims, and they are the brethren of the Devil (Shaytaan)!
Source: From the taped cassette (no.11), recorded in the month of Dhul-Hijjah 1408H (1987CE) at 'at-Tawiyyatul-Islaamiyyah'.