This OPCW report is about a year old, but whatever.
The IIT concludes that there are reasonable grounds to believe that, on 1 September 2015, between 09:00 and 12:00 (UTC+3), during sustained attacks aimed at capturing the town of Marea, units of the Islamic State in Iraq and the Levant (ISIL) deployed sulfur mustard, using one or more artillery guns.
There’s a wealth of material, including this account of ISIL CW manufacturing:
