Counter Terrorist Trends and Analyses (CTTA) – Volume 9, Issue 04 | RSIS

RSIS is a Singapore thinktank, and this is the quarterly CTTA that they put out. Recommend taking a look at Haniff Hassan's article in this and where he is focusing down on in it.
"IS also faces criticism from fellow jihadists, notably Al Qaeda Central and other rival groups such as Jabhah Al-Nusrah (now part of Hayat Tahrir al-Sham) and Al Qaeda in the Arabian Peninsula (AQAP).3 One of the many criticisms directed against IS is its permissiveness in the practice of takfir (declaring a Muslim as apostate). This makes IS a takfiri group that can be equated with the Kharijites, a rebellious group which has been denounced by Sunni Muslims since its emergence in 7th century Arabia. "