The website Jihad Watch published the full text of the ISIS declaration of responsibility for the Paris attacks -- chock-full of Islamic references -- and among the grievances it lists justifying the attack they say this:
“…the scent of death will not leave their nostrils… as long as they dare to curse our Prophet (blessings and peace upon him)…”
(As we know (or should know by now), that parenthetical “peace upon him” is obligatory for all Muslims to say when referring to Muhammad.)
I notice, however, when the New York Times reported it, they didn’t provide the full text, but rather carefully sidestepped and tip-toed around the Islamic content, cherry-picking quotes and paraphrasing. And, needless to say, they omitted the telling reference to Muhammad.